tests: add out_s3 retry_limit and multipart test coverage

Add retry_limit tests:
- putobject_retry_limit_semantics: verify retry_limit=1
  results in exactly 2 PutObject attempts
- default_retry_limit: verify default retry_limit (5)
  results in 6 PutObject attempts

Add assertions to all existing tests to verify the correct
S3 API path is exercised (PutObject vs multipart) and the
expected number of API calls are made.

Add preserve_data_ordering test to exercise the upload
queue path.

Use upload_timeout=6s with sleep(10) consistently so the
timer fires and exercises the real upload path. Add unique
store_dir via mkdtemp to multipart tests. Clean up all API
call counters at the end of each test.

All 15 tests pass under valgrind with 0 bytes definitely
lost.

Co-authored-by: Thean Lim <theanlim@amazon.com>
Signed-off-by: Anuj Singh <singholt@amazon.com>

Author: 2 people