Remove unnecessary allocation/copy from the string serialization implementation

[frankdavid]

Avoid creating an intermediate vector when serializing texts.

Affected benchmarks:

Benchmark: text
  total:
    instructions: 38.30 M (improved by 17.97%)
    heap_increase: 99 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 20.46 M (improved by 29.08%)
    heap_increase: 66 pages (improved by 33.33%)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 17.84 M (0.00%) (change within noise threshold)
    heap_increase: 33 pages (regressed from 0)
    stable_memory_increase: 0 pages (no change)

Benchmark: btreemap
  total:
    instructions: 19.75 B (improved by 2.44%)
    heap_increase: 1179 pages (1.29%) (change within noise threshold)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 4.02 B (improved by 10.70%)
    heap_increase: 159 pages (improved by 38.13%)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 15.72 B (-0.08%) (change within noise threshold)
    heap_increase: 1020 pages (regressed by 12.46%)
    stable_memory_increase: 0 pages (no change)

My assumption is that the heap_increase regression in the decoding phase is due to the fact that heap is not reclaimed after encoding. Since encoding uses less heap after this change, the heap increase for the decoding phase is now higher.

[github-actions]

Name	Max Mem (Kb)	Encode	Decode
blob	4_224	20_459_319 ($\textcolor{green}{-0.00\%}$)	12_083_390
btreemap	75_456 ($\textcolor{red}{1.29\%}$)	4_022_699_921 ($\textcolor{green}{-10.70\%}$)	15_709_219_501 ($\textcolor{green}{-0.08\%}$)
nns	192	2_257_486 ($\textcolor{green}{-0.96\%}$)	12_617_469 ($\textcolor{green}{-0.14\%}$)
nns_list_proposal	1_792	7_041_444 ($\textcolor{green}{-0.35\%}$)	187_610_779 ($\textcolor{red}{0.01\%}$)
option_list	576	7_141_454 ($\textcolor{red}{0.01\%}$)	32_450_234 ($\textcolor{red}{0.28\%}$)
text	6_336	20_455_442 ($\textcolor{green}{-29.08\%}$)	17_839_372 ($\textcolor{red}{0.00\%}$)
variant_list	128	7_142_657 ($\textcolor{red}{0.00\%}$)	24_608_159
vec_int16	16_704	168_582_443 ($\textcolor{green}{-0.00\%}$)	1_073_771_349

• Parser cost: 18_786_815 ($\textcolor{red}{0.00\%}$)
• Extra args: 3_254_228

Click to see raw report

---------------------------------------------------

Benchmark: blob
  total:
    instructions: 32.54 M (-0.00%) (change within noise threshold)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 20.46 M (-0.00%) (change within noise threshold)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 12.08 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: text
  total:
    instructions: 38.30 M (improved by 17.97%)
    heap_increase: 99 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 20.46 M (improved by 29.08%)
    heap_increase: 66 pages (improved by 33.33%)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 17.84 M (0.00%) (change within noise threshold)
    heap_increase: 33 pages (regressed from 0)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: vec_int16
  total:
    instructions: 1.24 B (-0.00%) (change within noise threshold)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 168.58 M (-0.00%) (change within noise threshold)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 1.07 B (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: btreemap
  total:
    instructions: 19.73 B (improved by 2.45%)
    heap_increase: 1179 pages (1.29%) (change within noise threshold)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 4.02 B (improved by 10.70%)
    heap_increase: 159 pages (improved by 38.13%)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 15.71 B (-0.08%) (change within noise threshold)
    heap_increase: 1020 pages (regressed by 12.46%)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: option_list
  total:
    instructions: 39.59 M (0.23%) (change within noise threshold)
    heap_increase: 9 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.14 M (0.01%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 32.45 M (0.28%) (change within noise threshold)
    heap_increase: 9 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: variant_list
  total:
    instructions: 31.75 M (0.00%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.14 M (0.00%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 24.61 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns
  total:
    instructions: 34.50 M (-0.11%) (change within noise threshold)
    heap_increase: 3 pages (no change)
    stable_memory_increase: 0 pages (no change)

  0. Parsing (scope):
    instructions: 18.79 M (0.00%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 2.26 M (-0.96%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 12.62 M (-0.14%) (change within noise threshold)
    heap_increase: 1 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns_list_proposal
  total:
    instructions: 194.65 M (-0.01%) (change within noise threshold)
    heap_increase: 28 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.04 M (-0.35%) (change within noise threshold)
    heap_increase: 3 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 187.61 M (0.01%) (change within noise threshold)
    heap_increase: 25 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: extra_args
  total:
    instructions: 3.25 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------
Successfully persisted results to canbench_results.yml

[chenyan-dfinity]

LGTM!