use workspace dependencies for tower

[GlenDC]

Closes #776

[GlenDC]

@tobz this would require a MSRV bump to 1.64 (currently it is 1.63): https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-164-2022-09-22

[tobz]

Seems fine to bump: 1.64 is still from September 2022 so we're far far ahead of the support window goal.

[GlenDC]

Seems fine to bump: 1.64 is still from September 2022 so we're far far ahead of the support window goal.

✅

[tobz]

Just fixed some conflicts and made some small tweaks in the process, namely using the short-form of the dtolnay/rust-toolchain action where you can pass the Rust toolchain version as the action version (i.e., you get the stable toolchain by using dtolnay/rust-toolchain@stable)