Implement BlockCache trait for FsBlockDb #6009

Job	Run time
Latest build on ubuntu-latest	2m 10s
Build target wasm32-wasi	52s
Latest build on windows-latest	5m 23s
Bitrot check	1m 39s
Check ZFuture build on Linux	27s
Clippy (MSRV)	1m 13s
Latest build on macOS-latest	1m 46s
Check ZFuture build on macOS	59s
Check ZFuture build on Windows	2m 38s
Clippy (beta)	12s
Code coverage	1h 4m 52s
Intra-doc links	2m 12s
Rustfmt	15s
protobuf consistency	1m 5s
UUID validity	7s
Test on Linux	4m 48s
Test Orchard on Linux	3m 52s
Test NU7 on Linux	3m 52s
Test on macOS	5m 4s
Test Orchard on macOS	5m 5s
Test on Windows	4m 54s
Test Orchard on Windows	2m 26s
Test NU7 on Windows	2m 34s
Required status checks have passed	3s
	1h 58m 28s

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