add benchmarks for coverlet.core and coverlet.msbuild

[Bertk]

Prepare benchmark tests for coverlet.core (currently uses InProcessToolchain)
=> could be used to monitor performance regressions

• add benchmarks tests
• fix build warnings
• partial update of nuget packages

Results for master branch (small updates for dotnet.benchmark)

Note

These benchmark test methods provide a baseline for performance monitoring. Future enhancements should include additional targeted tests for performance-critical code paths, focusing on areas like:

• Instrumentation of large assemblies
• Coverage data collection at runtime
• Hit data processing and report generation
• Memory allocation patterns

[Bertk]

Results for coverlet 6.0.1 release (small updates for dotnet.benchmark)

I use coverlet.core.benchmark.tests to identify the commit introducing the coverlet 6.0.2 performance regression (see PR #1689).

[Bertk]

Actual results for this PR (coverlet main branch) are: