Upgrade to Rust 1.95

[kailan]

No description provided.

[kpfleming]

Would you consider making a slightly different set of changes? With rust-toolchain.toml in place, there shouldn't be any need to specify a Rust version anywhere else (in configuration files or workflows), and there should not be any need to invoke rustup to install, uninstall, or set default either. That change would result in the version being specified in only one location and eliminate the risk of version mismatches.

We don't need to set rust-version in cli/Cargo.toml since that crate is not intended for re-use; for the top-level Cargo.toml (the viceroy-lib crate) the rust-version sets the MSRV for the crate, it does not specify the compiler version to be used when building it. That means it should be set to some reasonably recent version which is compatible with the source code, but doesn't need to be any newer.

If you'd prefer, I'd be happy to make the changes in this branch instead.

[kailan]

Would you consider making a slightly different set of changes? With rust-toolchain.toml in place, there shouldn't be any need to specify a Rust version anywhere else

I'll give it a go!

[kpfleming]

No harm making this change, but it doesn't appear that this Dockerfile is being used anywhere in the repository and it just builds a very simple image containing rustup and Rust.