FIX: Downloads features

[SMoraisAnsys]

Summary

This PR refactors the downloads module and improves test coverage.

Changes

The download logic in downloads.py has been reworked to use ansys-tools-common as the underlying download manager, replacing the previous custom implementation. This simplifies the codebase and reduces maintenance overhead.

A new test_downloads.py file provides unit tests for the download functions, including validation that deprecated functions properly emit warnings.

The test_utils.py file was moved from tests/utils/ to tests/unit/ to run with units tests. This was not tested in CI previously

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.23%. Comparing base (5cbae21) to head (b56d4a7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1885      +/-   ##
==========================================
+ Coverage   70.20%   70.23%   +0.03%     
==========================================
  Files         261      261              
  Lines       42416    42416              
==========================================
+ Hits        29779    29792      +13     
+ Misses      12637    12624      -13     

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