Update CI coverage: grcov/codecov

[samuel-jimenez]

-Zprofile support has been removed from Rust.
Instead of attempting to work around it (#2306), this patch switches the CI to use LLVM instrumentation-based coverage,
as recommended in grcov #1240.

Codecov syntax has been updated to v5. This action now requires a token to be set. This commit uses the CODECOV_TOKEN secret to hold this token. However, if desired, token use can be disabled per repository, or by configuring OIDC.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.25%. Comparing base (0cc0c62) to head (1d8c7b9).
Report is 152 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2348       +/-   ##
===========================================
+ Coverage   30.91%   62.25%   +31.34%     
===========================================
  Files          53       59        +6     
  Lines       20112    31043    +10931     
  Branches     9755        0     -9755     
===========================================
+ Hits         6217    19326    +13109     
- Misses       7922    11717     +3795     
+ Partials     5973        0     -5973     

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[sylvestre]

excellent, thanks!