Three recent PRs improve Leo's support for Rust

[Edward K. Ream]

Three recent PRs (all in "devel") improve how Leo imports and colorizes Rust:

- PR #4275 and PR #4278 fix bugs in Leo's Rust colorizer, including a gigantic speedup in all of Leo's colorizers when handling large text.

- PR #4277 fixes several annoying bugs in Leo's Rust importer. Leo now correctly imports all of the files in the Ruff project!

Discussion

At long last, Leonistas can import and study Rust code without annoying distractions:

- The Rust importer never generates too-large nodes.

- Leo colors all Rust syntax quickly and correctly.

These three PRs help me transition from working on Leo to working with Leo.

Please report any problems immediately.

Edward