Implement Read/Write for Pin<P> #2346

Job	Run time
Verify hyper.h is up to date	16s
Check Style	5s
features	16s
Test C API (FFI)	19s
Test with Miri	52s
minimal-versions	21s
Check MSRV	25s
udeps	22s
Test stable on ubuntu-latest	1m 21s
Test stable on windows-latest	3m 28s
Test stable on macOS-latest	2m 9s
Test beta on ubuntu-latest	1m 18s
Test beta on windows-latest	1m 59s
Test beta on macOS-latest	3m 16s
Test nightly on ubuntu-latest	1m 22s
Test nightly on windows-latest	2m 21s
Test nightly on macOS-latest	1m 57s
Build docs	16s
Check exposed types	24s
CI is green	1s
	22m 48s

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