chore: remove tower dep by vendoring Oneshot #483

Job	Run time
Check Style	9s
semver	15s
features	34s
Test with Miri	48s
Check MSRV (1.63)	51s
Test stable on ubuntu-latest	28s
Test stable on windows-latest	1m 50s
Test stable on macos-latest	29s
Test beta on ubuntu-latest	34s
Test beta on windows-latest	1m 8s
Test beta on macos-latest	41s
Test nightly on ubuntu-latest	32s
Test nightly on windows-latest	1m 12s
Test nightly on macos-latest	31s
Build docs	12s
CI is green	0s
	10m 14s

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