♻️ chore: remove mq-check and mq-docs crates
- Remove mq-check and mq-docs from workspace and dependencies
- Delete crates/mq-check and crates/mq-docs directories
- Update CI workflow, Cargo.toml, Cargo.lock, and related files
- Clean up built-in and section module comments
Removes deprecated CLI tools and cleans up workspace structure.
♻️ refactor(lang): organize constants into submodules and improve builtin variable scoping
Reorganize flat constants into `builtins` and `identifiers` submodules for better
code organization. Refactor builtin functions (take_while, group_by, fold, unique_by)
to use `do...end` blocks for proper mutable variable scoping.