feat: Improve Sharded Repodata Progress Message

[jjerphan]

Description

Example of message on cold cache:

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 10.20408% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.40%. Comparing base (f7d6d8e) to head (7827213).

Files with missing lines	Patch %	Lines
libmamba/src/core/output.cpp	12.00%	22 Missing ⚠️
libmamba/src/api/utils.cpp	0.00%	8 Missing ⚠️
libmamba/src/core/shard_index_loader.cpp	12.50%	7 Missing ⚠️
libmamba/src/core/shard_traversal.cpp	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4225      +/-   ##
==========================================
+ Coverage   52.73%   53.40%   +0.67%     
==========================================
  Files         240      240              
  Lines       29526    29567      +41     
  Branches     3154     3159       +5     
==========================================
+ Hits        15570    15790     +220     
+ Misses      13953    13774     -179     
  Partials        3        3              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.