### What's been done
- `subsystem-bench` has been split into two parts: a cli benchmark
runner and a library.
- The cli runner is quite simple. It just allows us to run `.yaml` based
test sequences. Now it should only be used to run benchmarks during
development.
- The library is used in the cli runner and in regression tests. Some
code is changed to make the library independent of the runner.
- Added first regression tests for availability read and write that
replicate existing test sequences.

### How we run regression tests
- Regression tests are simply rust integration tests without the
harnesses.
- They should only be compiled under the `subsystem-benchmarks` feature
to prevent them from running with other tests.
- This doesn't work when running tests with `nextest` in CI, so
additional filters have been added to the `nextest` runs.
- Each benchmark run takes a different time in the beginning, so we
"warm up" the tests until their CPU usage differs by only 1%.
- After the warm-up, we run the benchmarks a few more times and compare
the average with the exception using a precision.

### What is still wrong?
- I haven't managed to set up approval voting tests. The spread of their
results is too large and can't be narrowed down in a reasonable amount
of time in the warm-up phase.
- The tests start an unconfigurable prometheus endpoint inside, which
causes errors because they use the same 9999 port. I disable it with a
flag, but I think it's better to extract the endpoint launching outside
the test, as we already do with `valgrind` and `pyroscope`. But we still
use `prometheus` inside the tests.

### Future work
* https://github.com/paritytech/polkadot-sdk/issues/3528
* https://github.com/paritytech/polkadot-sdk/issues/3529
* https://github.com/paritytech/polkadot-sdk/issues/3530
* https://github.com/paritytech/polkadot-sdk/issues/3531

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Co-authored-by: Alexander Samusev <[email protected]>