optmize newest_rooted_write

[grooviegermanikus]

let slots_map_min_slot = *self.slots.keys().min().unwrap_or(&0u64);

+        #[inline(always)]
+        fn get_slot(slot: u64, slots: &HashMap<u64, SlotData>, min_slot: u64) -> Option<&SlotData> {
+            if slot < min_slot {
+                return None;
+            }
+            slots.get(&slot)
+        }

See branch hacking/slotmap-min