Add support for sha512, xxhash algorithms, and MD5 for httpchecksums

[SamRemis]

Description of changes:
This PR updates the flexible checksums feature to add support for SHA512, XXHASH64, XXHASH3, XXHASH128 as well as add support for passing MD5 through as a checksum to services where it is supported when pre-calculated by the user.

Included are some small refactorings such as updating some unit tests to use pytest.mark.parametrize to reduce code duplication as well as updating the private has_checksum_header function to use a new get_checksum_header and which returns a list of algorithms found in the checksum header.

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Codecov Report

❌ Patch coverage is 75.92593% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.62%. Comparing base (b0a4fbe) to head (f0d3290).
⚠️ Report is 311 commits behind head on develop.

Files with missing lines	Patch %	Lines
botocore/httpchecksum.py	71.73%	13 Missing ⚠️
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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3637      +/-   ##
===========================================
- Coverage    92.71%   92.62%   -0.10%     
===========================================
  Files           68       68              
  Lines        15561    15629      +68     
===========================================
+ Hits         14428    14476      +48     
- Misses        1133     1153      +20     

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[jonathan343]

Thanks Sam!

I think these changes look pretty good! I don't have much feedback other than improving the changelog entry description. Happy to approve when that's updated.

One question I do have is: Can you can remind me why we're not switching to the CRT implementation of SHA512 when installed in the customers environment?

[SamRemis]

Thanks Sam!

I think these changes look pretty good! I don't have much feedback other than improving the changelog entry description. Happy to approve when that's updated.

One question I do have is: Can you can remind me why we're not switching to the CRT implementation of SHA512 when installed in the customers environment?

https://github.com/awslabs/aws-crt-python/blob/d6ed76b4ed79ab694f852cdecec197690c861674/awscrt/checksums.py

As far as I know, it's not currently supported. I'll double check with the CRT team to make sure I'm not missing something prior to merging this PR