rework feature tracing experiments and time-stats table, add feature sampling experiment

[jonas-kaufmann]

Requires https://github.com/se-sic/VaRA/pull/972 and https://github.com/se-sic/vara-llvm-project/pull/84.

Even though this contains a lot of changes, the commit history is clean meaning each commit touches different files. I recommend reviewing based on that.

[codecov]

Codecov Report

Patch coverage: 48.67% and project coverage change: -0.13 ⚠️

Comparison is base (a9a3304) 67.09% compared to head (82891d3) 66.96%.

❗ Current head 82891d3 differs from pull request most recent head 4b764c6. Consider uploading reports for the commit 4b764c6 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##           vara-dev     #748      +/-   ##
============================================
- Coverage     67.09%   66.96%   -0.13%     
============================================
  Files           319      322       +3     
  Lines         24025    24225     +200     
============================================
+ Hits          16119    16222     +103     
- Misses         7906     8003      +97     

Impacted Files	Coverage Δ
varats-core/varats/experiment/experiment_util.py	64.58% <ø> (ø)
...ats/varats/experiments/vara/feature_perf_runner.py	44.44% <0.00%> (ø)
...arats/experiments/vara/instrumentation_verifier.py	48.00% <0.00%> (+1.84%)	⬆️
.../projects/perf_tests/feature_perf_cs_collection.py	58.13% <ø> (ø)
varats/varats/tools/bb_config.py	100.00% <ø> (ø)
varats/varats/tables/time_stats_table.py	43.24% <6.25%> (-0.88%)	⬇️
...rats/varats/experiments/vara/feature_experiment.py	40.71% <39.39%> (-0.52%)	⬇️
...ts/varats/experiments/vara/feature_perf_tracing.py	44.13% <44.13%> (ø)
varats/varats/tables/time_workloads.py	40.54% <50.00%> (ø)
...s/varats/experiments/vara/feature_perf_sampling.py	51.42% <51.42%> (ø)
... and 10 more

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[vulder]

Overall this looks quite good, I only found a few nits we should clean up before merging.