zcash_client_backend: Generalize & extend wallet metadata query API #6017

Job	Run time
Bitrot check	1m 30s
Build target wasm32-wasi	53s
Latest build on ubuntu-latest	2m 6s
Check ZFuture build on Linux	21s
Latest build on windows-latest	3m 41s
Clippy (MSRV)	1m 3s
Check ZFuture build on macOS	45s
Clippy (beta)	15s
Latest build on macOS-latest	2m 7s
Check ZFuture build on Windows	2m 50s
Code coverage	1h 6m 57s
Intra-doc links	2m 6s
Rustfmt	16s
protobuf consistency	1m 1s
UUID validity	7s
Test on Linux	9m 5s
Test Orchard on Linux	10m 44s
Test NU7 on Linux	8m 57s
Test on macOS	9m 43s
Test Orchard on macOS	12m 6s
Test on Windows	17m 15s
Test Orchard on Windows	21m 26s
Test NU7 on Windows	19m 16s
Required status checks have passed	1s
	3h 14m 31s

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