Replace bool-based settings with enums, refine visibility and
signatures, and standardize `Self` usage across the crate.

- Introduce `ErrorOutput`, `RenderOutput`, `PanicSilence`, `Verbosity`,
  `ColorOutput`, and `ProgressOutput` enums for clearer configuration
  semantics
- Make `GlobalResources`, `ProgramCell`, and
  `split_input`/`split_input_string` public
- Change hook info parameters to accept references and
  `split_input_string` to take `&str`
- Apply `Self` shorthand throughout implementations and add
  `#[must_use]` attributes where appropriate
- Enable strict clippy lints with targeted allowances

Fix the method to use `eprintln!` instead of `println!` when
`immediate_output` is enabled, ensuring error output goes to stderr.

Implement `RenderResult::append_other()` to merge buffered content and
immediate output behavior from one result into another. Add the
`r_append!` macro with both explicit buffer (`dst, src`) and implicit
buffer (`src`) usage forms, re-exported from `mingling::prelude`.

Remove `Deref<Target=str>` and `render_text:String` in favor of
`render_buffer:Vec<(String, RenderResultMode)>` and an
`immediate_output`
flag. Add `RenderResultMode` enum, `r_eprint!`/`r_eprintln!` macros, and
new buffer manipulation methods (`append_to_buffer`, `eprint`, etc.).
Update `Display` to trim output and remove trailing newline. Migrate all
callers and tests away from `Deref` usage.

Add `#![deny(missing_docs)]` across multiple crates and fill in
documentation for all public items, including struct fields, enum
variants, trait methods, and proc macros.  Also mark two shell scripts
as executable.

macros

Reintroduce `r_print!` and `r_println!` macros as public exports, now
supporting both explicit buffer argument and implicit `#[buffer]` attr.
Add `#[buffer]` attribute macro that wraps unit-returning functions to
produce a `RenderResult` with an automatically injected buffer variable.
Relax `RenderResult::print()` and `println()` to accept `impl
AsRef<str>`.