Move the REPL's argument splitting logic into a new public `utils`
module exposing the `ArgumentSplitter` trait for reuse by downstream
code.

Change `HookPreDispatchInfo.arguments` from `&[String]` to `&mut
Vec<String>`
so hooks can rewrite command-line arguments before dispatch.

Refactor program configuration types into a dedicated public `config`
module under `mingling_core`, making `StructuralRendererSetting`
accessible via `mingling_core::config` instead of the crate root.

Update all internal references and setup modules to use the new
`config::` path convention.

Mark all source files with a comment indicating they are not optimized
for documentation purposes.

Add `#[allow(clippy::future_not_send)]` to chain invocation methods and
clarify Send requirements for `exec` bounds.