Add a gitattributes file to specify LF line endings #316

Job	Run time
Test Suite (ubuntu-latest)	36s
Test Suite (stable)	35s
Test Suite (windows-latest)	1m 25s
Clippy (stable)	29s
Check (stable)	17s
Test Suite (stable, --no-default-features)	35s
Test Suite (macOS-latest)	1m 7s
Test Suite (stable, --features track-caller)	36s
Rustfmt (stable)	11s
Test Suite (stable, --features pyo3)	39s
Miri	1m 5s
Test Suite	4m 18s
Test Suite (stable, --features auto-install)	38s
Test Suite (--no-default-features)	4m 24s
Test Suite (stable, --all-features)	39s
Test Suite (--features track-caller)	4m 15s
Test Suite (beta)	36s
Test Suite (--features auto-install)	4m 31s
Test Suite (beta, --no-default-features)	35s
Test Suite (beta, --features track-caller)	35s
Test Suite (beta, --features pyo3)	39s
Test Suite (beta, --features auto-install)	36s
Test Suite (beta, --all-features)	37s
Test Suite (nightly)	45s
Test Suite (nightly, --no-default-features)	47s
Test Suite (nightly, --features track-caller)	47s
Test Suite (nightly, --features pyo3)	47s
Test Suite (nightly, --features auto-install)	44s
Test Suite (nightly, --all-features)	48s
	34m 36s

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