zcash_client_backend: Pure refactoring for note selection ergonomics. #5017

Job	Run time
Build target wasm32-wasi	1m 33s
Test on Linux	9m 22s
Test Orchard on Linux	6m 45s
Test NU6 on Linux	9m 15s
Bitrot check	1m 36s
Latest build on ubuntu-latest	1m 39s
Test on macOS	17m 46s
Check ZFuture build on Linux	23s
Test Orchard on macOS	24m 10s
Check ZFuture build on macOS	55s
Latest build on windows-latest	3m 4s
Clippy (MSRV)	2m 7s
Test on Windows	12m 44s
Check ZFuture build on Windows	1m 12s
Latest build on macOS-latest	3m 1s
Test Orchard on Windows	10m 55s
Test NU6 on Windows	13m 55s
Clippy (beta)	11s
Code coverage	17m 40s
Intra-doc links	2m 28s
Rustfmt	14s
protobuf consistency	1m 41s
UUID validity	3s
	2h 22m 39s

Provide feedback