chore: remove tower dep by vendoring Oneshot #484

Job	Run time
Check Style	5s
semver	14s
features	35s
Check MSRV (1.63)	50s
Test with Miri	50s
Test stable on ubuntu-latest	29s
Test stable on windows-latest	2m 35s
Test stable on macos-latest	34s
Test beta on ubuntu-latest	40s
Test beta on windows-latest	1m 16s
Test beta on macos-latest	48s
Test nightly on ubuntu-latest	31s
Test nightly on windows-latest	1m 36s
Test nightly on macos-latest	30s
Build docs	13s
CI is green	0s
	11m 46s

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