Fix singularities in `Quat::to_euler()` #1010

Job	Run time
Lint	3m 27s
Test portable simd (ubuntu-latest, nightly)	1m 12s
Test portable simd (macos-latest, nightly)	1m 33s
Test portable simd (windows-latest, nightly)	2m 19s
Test (ubuntu-latest, stable)	3m 31s
Test (ubuntu-latest, beta)	3m 13s
Test (ubuntu-latest, nightly)	3m 35s
Test (macos-latest, stable)	6m 14s
Test (macos-latest, beta)	6m 22s
Test (macos-latest, nightly)	6m 19s
Test (windows-latest, stable)	7m 7s
Test (windows-latest, beta)	5m 40s
Test (windows-latest, nightly)	6m 26s
Test wasm (stable, ubuntu-latest)	5m 24s
	1h 2m 22s

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