Jack Grigg

[Rebased on `main`](https://github.com/zcash/librustzcash/compare/c83b443770ac01caa33c2539b715058637cfde76..2d098342dd5c86414e645a8f85ed6816ae756a5e) to use the new `BlockCache` trait. I still need to replace the `anyhow` usage with typed errors, and migrate the previous `FsBlockDb`-specific code into `zcash_client_sqlite`.

[Force-pushed](https://github.com/zcash/librustzcash/compare/2d098342dd5c86414e645a8f85ed6816ae756a5e..24277a6ba4013ead9a385acceff6db3de7a0c198) to fix failing tests, and implement an `Error` enum to replace `anyhow` usage.