Rust

Extract `optional_time_delta` for sharing #40195

Job	Run time
check-features	7m 6s
check-style	18s
check-omicron-deployment (ubuntu-22.04)	3m 1s
build-docs	4m 9s
check-omicron-deployment (macos-14)	5m 34s
clippy-lint	5m 42s
	25m 50s

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