Add `Vector2D.to_isize()` and `Vector3D.to_isize()` (closes #535) #125

Job	Run time
Check code formatting	2s
Linux (1.56.0)	53s
Linux (stable)	21s
Linux (beta)	20s
Linux (nightly)	18s
Linux (--features serde, 1.56.0)	1m 3s
Linux (--features serde, stable)	26s
Linux (--features serde, beta)	23s
Linux (--features serde, nightly)	24s
Linux (--no-default-features --features libm, 1.56.0)	52s
Linux (--no-default-features --features libm, stable)	24s
Linux (--no-default-features --features libm, beta)	18s
Linux (--no-default-features --features libm, nightly)	16s
Linux (stable, --features mint)	23s
Linux (stable, --features bytemuck)	12s
Linux (stable, --features arbitrary)	12s
Linux (nightly, --features unstable)	19s
Linux (nightly, --features unstable,serde)	22s
Result	1s
	7m 29s

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