feat: Prefilter Shard Records on Python Minor Version

[jjerphan]

Description

Comes after #4187 and #4220.

Since the minor versions python is pinned in users' environments, we can prefilter records in shards using it to only selected relevant builds.

This definitely eases the installation of packages depending on python, by reducing the number of clauses within the solver and thus the time spent and RAM used resolving the environments. For instance for pyarrow, it reduces the time spent by 5 and the memory footprint by 20.

If python is not installed, we first try to prefilter builds depending on a fallback minor version (python 3.14 proposed), before potentially retrying without (current behavior) if this fallback minor version cannot be used.

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 44.44444% with 95 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.72%. Comparing base (39702c7) to head (a4e0425).

Files with missing lines	Patch %	Lines
libmamba/src/api/utils.cpp	15.71%	59 Missing ⚠️
libmamba/src/api/install.cpp	0.00%	15 Missing ⚠️
libmamba/src/core/shards.cpp	75.00%	9 Missing ⚠️
libmamba/src/api/channel_loader.cpp	33.33%	6 Missing ⚠️
libmamba/src/api/update.cpp	0.00%	3 Missing ⚠️
libmamba/src/core/shard_python_minor_prefilter.cpp	92.10%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4214      +/-   ##
==========================================
- Coverage   53.65%   52.72%   -0.93%     
==========================================
  Files         239      240       +1     
  Lines       29349    29510     +161     
  Branches     3122     3151      +29     
==========================================
- Hits        15747    15559     -188     
- Misses      13599    13948     +349     
  Partials        3        3              

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[jjerphan]

Are there utilities we could reuse instead?

[jjerphan]

PrefixData could be reused, but this would be much more costly (because it parses all the installed packages JSON and convert them to PackageInfo). We only need one specs::Version here.