pczt: Add no-std support #6273

Job	Run time
Bitrot check	1m 31s
Latest build on ubuntu-latest	1m 55s
Build target wasm32-wasi	54s
Latest build on windows-latest	1m 37s
Latest build on macOS-latest	1m 39s
Check ZFuture build on Linux	1m 40s
Check ZFuture build on macOS	9s
Check ZFuture build on Windows	1m 40s
Clippy (MSRV)	1m 26s
Clippy (beta)	13s
Code coverage	3m 30s
Intra-doc links	2m 20s
Rustfmt	14s
protobuf consistency	1m 6s
Test no-Orchard on Linux	2m 35s
Test Orchard on Linux	2m 30s
Test no-Orchard on macOS	3m 25s
Test NU7 on Linux	2m 33s
Test Orchard on macOS	3m 27s
Slow Test Orchard on Linux	2m 37s
Test no-Orchard on Windows	5m 31s
Slow Test NU7 on Linux	2m 42s
Test Orchard on Windows	5m 46s
Test NU7 on Windows	6m 15s
UUID validity	4s
Required status checks have passed	1s
	57m 20s

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