zcash_client_backend: Add Orchard support to batch scanning. #2502

Job	Run time
Clippy (MSRV)	4m 27s
Build target wasm32-wasi	4m 6s
Latest build on ubuntu-latest	1m 30s
Bitrot check	5m 16s
Latest build on windows-latest	1m 33s
Clippy (beta)	14s
Code coverage	8m 36s
Latest build on macOS-latest	1m 46s
Intra-doc links	5m 1s
Rustfmt	12s
protobuf consistency	4m 12s
Test on ubuntu-latest	6m 52s
UUID validity	3s
Test on ubuntu-latest with --features orchard	7m 10s
Test on ubuntu-latest with --features unstable-nu6	7m 4s
Test on ubuntu-latest with --features zfuture	6m 55s
Test on windows-latest	6m 52s
Test on windows-latest with --features orchard	6m 54s
Test on windows-latest with --features unstable-nu6	6m 54s
Test on windows-latest with --features zfuture	6m 26s
Test on macOS-latest	7m 10s
Test on macOS-latest with --features orchard	7m 10s
	1h 46m 23s

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