feat: export legacy::ResponseFuture (#75) #233

Job	Run time
Check Style	13s
features	45s
Check MSRV (1.63)	55s
Test with Miri	44s
Test stable on ubuntu-latest	29s
Test stable on windows-latest	1m 15s
Test stable on macOS-latest	57s
Test beta on ubuntu-latest	31s
Test beta on windows-latest	1m 14s
Test beta on macOS-latest	44s
Test nightly on ubuntu-latest	30s
Test nightly on windows-latest	1m 21s
Test nightly on macOS-latest	46s
Build docs	20s
CI is green	1s
	10m 45s

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