[WIP] Alternative fix for `stdout`/`stderr` redirects

[kenodegard]

An alternative to #25.

Benefits (?) of this implementation:

• for tests marked as benchmarks (no fixture), the cache priming doesn't result in the same scope being run twice, e.g. the following works now:

  @pytest.mark.benchmark
  def test_tmp_path(tmp_path):
      (tmp_path / "random").mkdir()

  this is accomplished via code borrowed from pytest-rerunfailures, see pytest_codspeed.plugin.prime_cache

Submitting to see benchmark results.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #31 will improve performances by 6.37%

_{Comparing kenodegard:fix-outerr-redirects-alternative (8541559) with master (90e639b)}

Summary

⚡ 2 improvements ✅ 3 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	kenodegard:fix-outerr-redirects-alternative	Change
⚡	test_iterative_fibo_10	45.5 µs	42.7 µs	+6.37%
⚡	test_recursive_cached_fibo_10	113.8 µs	111.3 µs	+2.25%

[kenodegard]

Closing in favor of #32