Use 1 array for part info, instead of separate etag array and checksum array

[graebm]

Issue:
I wanted to track more info about each part. We already had separate arrays for the parts' etags and checksums, and the code to deal with them was always finicky since parts may arrive out of order and the array-list API is clunky.

Description of changes:
Use a single array-list to track all part info, instead of separate arrays for etags, checksums, size, etc

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

[codecov-commenter]

Codecov Report

Merging #322 (1766f7d) into main (28f7b87) will decrease coverage by 0.01%.
The diff coverage is 96.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #322      +/-   ##
==========================================
- Coverage   88.88%   88.87%   -0.01%     
==========================================
  Files          17       17              
  Lines        4947     4943       -4     
==========================================
- Hits         4397     4393       -4     
  Misses        550      550              

Impacted Files	Coverage Δ
source/s3_client.c	88.02% <ø> (ø)
source/s3_auto_ranged_put.c	92.15% <95.00%> (-0.10%)	⬇️
source/s3_copy_object.c	81.27% <100.00%> (+0.44%)	⬆️
source/s3_request_messages.c	74.76% <100.00%> (-0.12%)	⬇️