zcash_client_backend: Make VKs optional for PCZT extraction #6546

Job	Run time
Test no-Orchard on Linux	4m 34s
Test Orchard on Linux	6m 24s
Test NU7 on Linux	6m 26s
Bitrot check	1m 11s
Latest build on ubuntu-latest	1m 47s
Latest build on windows-latest	6m 13s
Latest build on macOS-latest	1m 36s
Build target wasm32-wasi	55s
Build target thumbv7em-none-eabihf	36s
Check ZFuture build on Linux	24s
Test no-Orchard on macOS	7m 36s
Check ZFuture build on macOS	37s
Slow Test Orchard on Linux	4m 33s
Test Orchard on macOS	7m 47s
Clippy (MSRV)	1m 14s
Check ZFuture build on Windows	2m 48s
Slow Test NU7 on Linux	4m 23s
Test no-Orchard on Windows	7m 54s
Test Orchard on Windows	12m 55s
Test NU7 on Windows	13m 16s
Clippy (beta)	12s
Intra-doc links	2m 9s
Code coverage	1h 19m 32s
Rustfmt	14s
protobuf consistency	1m 1s
UUID validity	4s
Required status checks have passed	2s
	2h 56m 23s

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