zcash_client_backend: Generalize & extend wallet metadata query API #6045

Job	Run time
Check ZFuture build on Linux	27s
Test on Linux	6m 17s
Check ZFuture build on macOS	36s
Test Orchard on Linux	7m 57s
Bitrot check	1m 35s
Check ZFuture build on Windows	1m 44s
Test NU7 on Linux	6m 24s
Test on macOS	7m 40s
Test Orchard on macOS	9m 59s
Build target wasm32-wasi	53s
Latest build on ubuntu-latest	1m 58s
Test on Windows	13m 4s
Test Orchard on Windows	15m 40s
Latest build on windows-latest	5m 9s
Clippy (MSRV)	1m 17s
Latest build on macOS-latest	1m 53s
Test NU7 on Windows	15m 29s
Clippy (beta)	13s
Code coverage	1h 4m 37s
Intra-doc links	2m 8s
Rustfmt	12s
protobuf consistency	1m 7s
UUID validity	3s
Required status checks have passed	4s
	2h 46m 26s

Provide feedback