feat: Add concurrent integration test & utils

[sichanyoo]

Issue #

#1561

Description of changes

• Adds utility functions (one that takes in variadic args and one that doesn't) that concurrently runs a passed-in function count number of times, idea taken from draft PR: feat: Add concurrent integration tests #1484
• Adds integration test for S3 that puts & gets 1MB files and runs them 100 times concurrently

New/existing dependencies impact assessment, if applicable

Conventional Commits

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jbelkins]

The rest of this is fine, but let's not commit 100MB of garbage to the project. Try generating that data in a temp dir, then using that in the test.

[jbelkins]

See individual comments

[jbelkins]

One question

[jbelkins]

Tests still seem to take quite a while (10 sec per test on Linux+CRT, 30 per sec on Mac+URLSession) but I'm approving because the tests do what they are supposed to do.

If we want to adjust the number of concurrent runs or the test duration, we can do that at a later time.