Improve reflow performance and general memory usage by reducing size of TerminalCharacter

[aidanhs]

cc #2622
This PR probably moves zellij to 'good enough for me' that it won't completely lock up on long lines.

Third in a series: #3045, #3032, #3043 (this pr)
This PR builds on the first+second and contains all commits from them - it will be easier to review after merge of the of them both.

There is a refactor (enabled by the previous PR in the series) to merge the two separate branches (new_columns != self.width + new_height != self.height) for viewport transfer.

The primary optimisation pursued here is in reducing the size of TerminalCharacter so the memory copies performed when reflowing are much cheaper. This also has the nice side effect of reducing overall memory usage.

I also added a few minor cleanups I noticed, and made zellij-utils stop unconditionally rebuilding.

I highly recommend reviewing these changes commit-by-commit, as I've carefully tried to make each one standalone and self-consistent.

[crabdancing]

Someone please merge this. I am suffering Y~Y

Edit: Since this repo doesn't have a Nix flake -- for any NixOS users interested, here's an standalone overlay to compile this against upstream nixpkgs:

  (self: super: {
    zellij = super.zellij.overrideAttrs (fAttrs: pAttrs: (let
      name = "zellij";
      owner = "aidanhs";
      repo = name;
      rev = "aphs-improve-reflow-perf-2";
      hash = "sha256-vIF17qMNmUCJ432KTzZoSoV2dCNCRv9WqvAVp4TLOjU=";
      depHash = "sha256-RGQe0fSnNYCDBhJ5pGbm7TPSoRa9x60NlGo3rgTJD6Y=";
      src = self.fetchFromGitHub {
        inherit owner repo rev hash;
      };
      cargoDeps = pAttrs.cargoDeps.overrideAttrs (lib.const {
        name = "${name}-vendor.tar.gz";
        inherit src;
        outputHash = depHash; 
      });
    in {
      inherit src cargoDeps;
    }));
  })

[imsnif]

Hey @aidanhs - I'm now merging this third and final PR in the series.

I wanted to thank you for your hard and excellent work on this. I changed some minor stuff (namely making sure integers don't overflow in some edge cases as well as removing the hard-coded unreachable crash with an error log, the latter because I don't want to trust anyone's memory about the way the code should flow when changes are made years from now).

This PR series solved some ingrained problem in an ancient part of the code base, improved our resource utilization and boosted our performance significantly. It also had the upshot of teaching me some really nice tricks in Rust which I was unaware of before :)

Also - thanks for the conditional compilation of our protobuf assets - that will certainly improve the development experience in this repository!

Cheers, and thanks again.

[aidanhs]

@imsnif a huge thanks to you for your quick turnaround on the multiple PRs!

I know that new contributors dropping big contributions can be disruptive, especially if the changes 1) aren't quite in line with a roadmap, 2) are complex and 3) haven't been discussed beforehand!
(apologies on 3, I didn't even know if I was going to be able to achieve a speedup - by the time I'd made progress worth noting, the PR was basically done)

So it's hugely appreciated (and a huge credit to you) that you've got through these so quickly, and it's very motivating if I want to contribute in the future.

I'll put some notes in the linked issue #2622 about the progress that's been made.

[crabdancing]

Praise be, aidanhs's salvation is upon us. 🙏