Refactor: Replace unbounded thread spawning with rayon parallel iterators #1204

Job	Run time
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	4m 18s
Tests (macos-latest, x86_64-apple-darwin, yes)	17m 4s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	8m 36s
Builds (windows-latest, aarch64-pc-windows-msvc)	5m 12s
Tests (macos-14, aarch64-apple-darwin, yes)	12m 26s
Builds (windows-latest, x86_64-pc-windows-msvc)	5m 2s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 30s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	7m 26s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	2m 3s
Builds (macos-14, aarch64-apple-darwin, yes)	4m 29s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	5m 22s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 17s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 45s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	6m 21s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	6m 10s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 32s
Builds (macos-latest, x86_64-apple-darwin, yes)	2m 20s
	1h 37m 53s

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