Jack Grigg

This PR can be closed as replaced by #588 and #589.

[Rebased on `main`](https://github.com/zcash/librustzcash/compare/4995d682391ca3d2cc8e6f9ab80bf93504ecb53b..c91dc38d0b0f7b8e359dd77900f3f68394e07229) to fix major merge conflicts after the test framework was moved out of `zcash_client_sqlite`. I'm going to perform more rebases on this to clean up the commit...

[Rebased on `main`](https://github.com/zcash/librustzcash/compare/c91dc38d0b0f7b8e359dd77900f3f68394e07229..1675bf39951b375e556037815b0c848853182709) to fix more merge conflicts.

[Force-pushed](https://github.com/zcash/librustzcash/compare/1675bf39951b375e556037815b0c848853182709..2c32c7387a1f10ac25e2d528712fde41c255884a) to refactor the commits without any changes. In particular, I've pulled most of the `async` test changes out into a final commit, because I do not want the test...

[Rebased on `main`](https://github.com/zcash/librustzcash/compare/2c32c7387a1f10ac25e2d528712fde41c255884a..890fd86c3e6e1841d6ca3966317c82b7b7490b30) to move away from the `async-trait` crate. I also did some more reworking of the commits to split them into logical changes. I almost have the test...

[Force-pushed](https://github.com/zcash/librustzcash/compare/890fd86c3e6e1841d6ca3966317c82b7b7490b30..020438cc0547dc9ea64341794917c76748fcff49) to remove the dependency of `BlockSource` on `data_api::chain::Error`, and thus remove the similar complexity that this PR added to `BlockCache`.

> Note to self: see how [Sign Mode Textual](https://twitter.com/simon_warta/status/1626255663650201604) might be useful in this context. _Originally posted in https://github.com/zcash/zips/issues/426#issuecomment-1433529601_

As the breakages aren't currently blocking for me, I'm happy to leave my `rustup` installation as-is and do more investigation of it if the `rustup` devs think it would be...

I just tried running `cargo +1.65.0 --version` to force the override, and got this: ``` $ cargo +1.65.0 --version error: no such command: `+1.65.0` Cargo does not handle `+toolchain` directives....

I initially guessed that `rustup` might be configuring my `PATH` here: ``` $ cat ~/.profile export PATH="$HOME/bin:$PATH" export PATH="$HOME/go/bin:$PATH" . "$HOME/.cargo/env" ``` However, there are two problems with that guess:...