Remove dependency on waker-fn #670

Job	Run time
cross (ubuntu-latest)	2m 5s
cross (macos-latest)	33s
clippy	24s
msrv (ubuntu-latest, 1.63)	1m 53s
fmt	3s
security_audit	8s
msrv (windows-latest, 1.63)	2m 4s
test (ubuntu-latest, nightly)	1m 9s
test (ubuntu-latest, beta)	1m 4s
windows_gnu (nightly, x86_64-pc-windows-gnu)	1m 59s
test (ubuntu-latest, stable)	58s
test (windows-latest, nightly)	2m 18s
test (windows-latest, beta)	1m 27s
test (windows-latest, stable)	3m 2s
test (macos-latest, nightly)	1m 37s
test (macos-latest, beta)	1m 5s
test (macos-latest, stable)	1m 18s
	23m 7s

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