Adding unit tests for sha256

[korjeek]

Adding comprehensive unit tests for SHA-256 implementation.

These tests verify:

1. Basic functionality with known test vectors (e.g., "abc")
2. Handling of large input data (4KB repeated 1000 times)
3. Edge case with repeated single-byte input (1 million 'a' characters)

The tests ensure compatibility with standard SHA-256 implementations and will help detect regressions during future code changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.23%. Comparing base (8d562d2) to head (90f2407).
⚠️ Report is 1 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2632      +/-   ##
============================================
+ Coverage     72.22%   72.23%   +0.01%     
============================================
  Files           127      127              
  Lines         70936    70936              
============================================
+ Hits          51232    51244      +12     
+ Misses        19704    19692      -12     

see 12 files with indirect coverage changes

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[ranshid]

Looks fine. I am not against adding these tests (maybe they can help in a future need to change the sha256 implementation...) biut can you please through some words on the top comment to explain what you are adding and why?

[ranshid]

Thank you @korjeek I meant the top comment :) , but adding these comments in the test file also works.
I edited the top comment as well. the reason is that the top comment is used as the final commit message. it is better to have some content attached to each commit.

[ranshid]

@korjeek can you PTAL at the test failures and fix?

[korjeek]

@korjeek can you PTAL at the test failures and fix?

seems like I fixed it