perf: Speed up `dt.offset_by` 2x for constant durations #8848

Job	Run time
test (ubuntu-latest)	3m 53s
integration-test (ubuntu-latest)	1m 48s
test (windows-latest)	8m 36s
check-features	7m 35s
integration-test (windows-latest)	4m 32s
check-wasm	5m 25s
	31m 49s

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