feat: Shard Caching

[jjerphan]

Description

Comes after #4162.

Type of Change

• Bugfix
• Feature / enhancement
• CI / Documentation
• Maintenance

Checklist

• My code follows the general style and conventions of the codebase, ensuring consistency
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run pre-commit run --all locally in the source folder and confirmed that there are no linter errors.
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[codecov]

Codecov Report

❌ Patch coverage is 85.33333% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.88%. Comparing base (35a3553) to head (431a307).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
libmamba/src/core/shards.cpp	85.33%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4174      +/-   ##
==========================================
+ Coverage   52.30%   52.88%   +0.57%     
==========================================
  Files         239      239              
  Lines       29088    29137      +49     
  Branches     3082     3090       +8     
==========================================
+ Hits        15215    15409     +194     
+ Misses      13870    13725     -145     
  Partials        3        3              

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