Helix to add Steel Scheme plugin system

Helix's pivot to Lisp/Scheme for extensibility is a brilliant design choice that reinforces its modal, structured editing philosophy, even if Scheme's syntax might alienate developers used to Lua or JavaScript.

• –Steel Scheme is written in Rust, allowing tight, zero-cost integration and sandboxing within Helix's core.
• –Lisp dialects are inherently suited for AST manipulation and structural editing, matching Helix's Kakoune-inspired selection-first design.
• –Transitioning away from pure native Rust features prevents the editor from bloating while satisfying the community's most requested capability.
• –Adoption might face a steeper learning curve compared to Neovim's Lua or VS Code's JavaScript, potentially limiting the initial extension library.