Replace `ThisProgram` with `Self` where appropriate and
mark constructors as `#[must_use]` and `const` where possible.
Simplify explicit lifetimes in `ProgramSetup` and `Default`
implementations using elided lifetimes.

Update stdout and error output settings to use explicit `RenderOutput`
and `ErrorOutput` enums, and replace the `confirm` boolean with distinct
`ConfirmationMode`, `InteractionMode`, and `YesAssumption` fields for
clearer control flow.

Add `Metadata<B>` trait and `#[metadata(Entry)]` attribute macro
to attach arbitrary, compile-time-typed metadata to entries.
Implement `ProgramCollect::get_metadata<T>()` for runtime retrieval,
backed by a global registry populated by `register_metadata!`.

Extend `pathf` with `MetadataPattern` to resolve metadata types
across modules at build time. Add two examples demonstrating
metadata usage with and without pathf integration.

trait

Rename the internal fallback type and its associated `ProgramCollect`
plumbing from `ErrorDispatcherNotFound`/`build_dispatcher_not_found` to
`EntryFallback`/`build_entry_fallback`, along with the generated enum
variant and pack type. Update all documentation, examples, and tests
accordingly.