Refactor #[chain], #[renderer], #[help], and #[completion] macros to
keep
the original user function as a named item instead of inlining its body.
Trait method implementations now call the original function by name,
injecting resources from the application context.

This improves debugging (stack traces reference user function names),
error messages, and macro expansion clarity.

Restructure flat module layout into logical directories (attr/, derive/,
func/, systems/, extensions/, utils.rs). Tighten internal function
visibility to pub(crate). All public API signatures remain unchanged.