Absolve kdl-rs of syn

[TheLostLambda]

This adds a few more manual impls in a couple of files, but nets us faster compile times and makes kdl-rs something that can be used as a dependency of facet-kdl in the future (facet-rs/facet#387).

It also fixes a bug where the Severity of KdlDiagnostics was always ignored.

A final comparison of compile times before and after this change will wait until zkat/miette#436 is released on crates.io (since I think using Git dependencies slows down Cargo a bit?)

The final dependency tree is:

[TheLostLambda]

@zkat I think I'll need your guidance on how to fix CI here — it's another case of being broken on main. It's because kdl-lsp is bringing in tower-lsp which is eventually bringing in [email protected] which needs Rust 1.81.1...

Is the kdl-lsp crate currently included in kdl-rss 1.17.1 MSRV, or should the CI be changed to ignore it when building with 1.17.1?

[zkat]

Just bump the MSRV, it's fine

[TheLostLambda]

Needed to update the configuration for cargo-dist too, since axodotdev/cargo-dist#1760 hasn't been fixed yet and GitHub wouldn't run the Plan action. Things are all green now!

[zkat]

@TheLostLambda [email protected] is tagged and released

[TheLostLambda]

Some more modest compile-time improvements than we saw in miette, but not bad overall! Plus, we've fixed a bug and added some tests whilst we were at it!

23% improvement in debug build times, and 10% in release!

[jplatte]

Would love to see this on crates.io, is a release going out soon-ish? :)