Optimize flattening in apache airflow workspace

[konstin]

Motivation

No-op uv lock in apache airflow (891c67f210ab7c877d1f00ea6ea3d3cdbb0e96ef) is slow, which makes uv run slow, too.

Reference project:

$ hyperfine "uv run python -c \"print('hi')\""
Benchmark 1: uv run python -c "print('hi')"
Time (mean ± σ):      16.3 ms ±   1.5 ms    [User: 9.8 ms, System: 6.4 ms]
Range (min … max):    13.0 ms …  20.0 ms    186 runs

Apache airflow before:

$ hyperfine "uv run python -c \"print('hi')\""
Benchmark 1: uv run python -c "print('hi')"
Time (mean ± σ):     161.0 ms ±   5.2 ms    [User: 135.3 ms, System: 24.1 ms]
Range (min … max):   155.0 ms … 176.3 ms    18 runs

Optimization

FlatRequiresDist::from_requirements is taking 50% of main thread runtime.

Before:

After both commits:

Apache airflow after the first commit:

$ hyperfine "uv-profiling run python -c \"print('hi')\""
Benchmark 1: uv-profiling run python -c "print('hi')"
  Time (mean ± σ):     122.3 ms ±   5.4 ms    [User: 96.1 ms, System: 24.7 ms]
  Range (min … max):   114.0 ms … 133.2 ms    23 runs

Apache airflow after the second commit:

$ hyperfine "uv-profiling run python -c \"print('hi')\""
Benchmark 1: uv-profiling run python -c "print('hi')"
  Time (mean ± σ):     108.5 ms ±   3.4 ms    [User: 83.2 ms, System: 24.2 ms]
  Range (min … max):   103.6 ms … 119.9 ms    28 runs

[konstin]

If we didn't go through the DNF for the general top level marker case this could be a &'static ExtraName