zcash_client_backend: Return decoding errors from `BatchRunners::add_… #2508

Job	Run time
Bitrot check	4m 19s
Latest build on ubuntu-latest	1m 55s
Latest build on windows-latest	4m 7s
Clippy (MSRV)	5m 21s
Build target wasm32-wasi	4m 1s
Latest build on macOS-latest	2m 17s
Code coverage	12m 3s
Intra-doc links	5m 1s
Rustfmt	11s
protobuf consistency	4m 11s
Test on ubuntu-latest	8m 44s
Test on ubuntu-latest with --features orchard	8m 42s
UUID validity	2s
Clippy (beta)	13s
Test on ubuntu-latest with --features unstable-nu6	8m 33s
Test on ubuntu-latest with --features zfuture	8m 48s
Test on windows-latest	8m 33s
Test on windows-latest with --features orchard	8m 35s
Test on windows-latest with --features unstable-nu6	8m 26s
Test on windows-latest with --features zfuture	8m 11s
Test on macOS-latest	8m 46s
Test on macOS-latest with --features orchard	8m 52s
	2h 9m 51s

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