Add `Debug` and `ApproxEq` impls for Rotation2D #98

Job	Run time
Check code formatting	11s
Linux (1.56.0)	1m 45s
Linux (stable)	12s
Linux (beta)	21s
Linux (nightly)	17s
Linux (--features serde, 1.56.0)	1m 59s
Linux (--features serde, stable)	19s
Linux (--features serde, beta)	23s
Linux (--features serde, nightly)	24s
Linux (--no-default-features --features libm, 1.56.0)	1m 38s
Linux (--no-default-features --features libm, stable)	15s
Linux (--no-default-features --features libm, beta)	18s
Linux (--no-default-features --features libm, nightly)	16s
Linux (stable, --features mint)	12s
Linux (stable, --features bytemuck)	13s
Linux (stable, --features arbitrary)	24s
Linux (nightly, --features unstable)	17s
Linux (nightly, --features unstable,serde)	21s
Result	1s
	9m 46s

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