feat: Avoid spawning async-io thread if possible #965

Job	Run time
windows_gnu (nightly, x86_64-pc-windows-gnu)	1m 29s
msrv (ubuntu-latest)	1m 11s
cross (macos-latest, stable)	2m 2s
msrv (windows-latest)	37s
cross (ubuntu-latest, stable)	1m 8s
wine	1m 46s
cross (ubuntu-latest, nightly)	1m 8s
cross (macos-latest, nightly)	2m 13s
security_audit / security_audit	18s
clippy / clippy	26s
fmt / fmt	15s
test (ubuntu-latest, stable)	55s
test (windows-latest, beta)	2m 4s
test (macos-latest, stable)	1m 18s
test (windows-latest, nightly)	1m 40s
test (ubuntu-latest, beta)	54s
test (ubuntu-latest, nightly)	56s
test (macos-latest, beta)	55s
test (macos-latest, nightly)	1m 1s
test (windows-latest, stable)	2m 4s
	24m 20s

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