Add discard_overstep function to Time<Fixed> #32044

Job	Run time
check-bevy-internal-imports	4s
build (windows-latest)	3m 54s
check-doc	5m 27s
build (ubuntu-latest)	3m 33s
check-missing-examples-in-docs	27s
ci	2m 7s
build (macos-latest)	4m 17s
miri	7m 17s
run-examples-on-windows-dx12	17m 42s
check-missing-features-in-docs	32s
markdownlint	1m 45s
check-compiles	3m 24s
msrv	59s
build-wasm	47s
	52m 15s

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