build(cargo): Update Rust toolchain to 1.90.0

[har7an]

Replace the previously used (and now EOL) Rust toolchain 1.84.0 with the currently stable 1.90.0. The versions in between didn't bring any radically new changes that affect our code as far as I could tell. However, there has been a significant improvement in development iteration times. See more on that below.

Apart from that, I took the time to deduplicate some of our cargo manifest keys, including crate licenses and rust versions. This change is made in a spirit similar to #4085, where I did pretty much the same with our crate dependencies. During this migration I noticed that the plugin-manager and session-manager were still using the 2018 Rust edition. I updated both crates to use Rust edition 2021 like the rest of the codebase does. Finally, this removes an obsolete build script that had been introduced during the migration from makers to cargo xtask to handle protobuf compilation for the WASM plugins.

Development Performance Improvements

Rust 1.90.0 brings in a very nice change: The default linker on Linux GNU is now lld. I ran a little benchmark to verify this. First I did a cargo clean && cargo xtask build to make sure all dependencies were built already. Then I wrote a script called bench.sh with the following content:

#!/usr/bin/env bash

cargo clean -p "zellij"
exec cargo build

Sidenote: Running this in a shell of course adds overhead to execution times from shell stuff, but in this case the runtime of linking far surpasses any shell setup so this is fine.

Tested on the HEAD commit of this branch this was the result:

$ hyperfine ./bench.sh
Benchmark 1: ./bench.sh
  Time (mean ± σ):      3.275 s ±  0.310 s    [User: 6.280 s, System: 5.697 s]
  Range (min … max):    3.058 s …  4.036 s    10 runs

Whereas with Rust 1.89.0 (commit fec4e69), this is what I got:

$ hyperfine ./bench.sh
Benchmark 1: ./bench.sh
  Time (mean ± σ):     17.478 s ±  0.658 s    [User: 12.322 s, System: 5.505 s]
  Range (min … max):   16.487 s … 18.412 s    10 runs

So in essence, iteration times should be significantly faster now. Similar improvements can be seen when using cargo q or cargo xtask build --quick-run. Yay!