The legacy `parser` feature and its module tree (`mingling::parser`,
`Argument`, `Picker`, `Pickable`, etc.) have been fully removed and
replaced by the `picker` feature powered by `arg-picker`.

BREAKING CHANGE: Remove `parser` feature and use `picker` instead.
Migration guide: Replace `features = ["parser"]` with
`features = ["picker"]` and update API usage per the provided table.

The `dispatcher!` macro no longer requires a `CMD*` dispatcher type
argument; the dispatcher struct is now generated internally as
`__Dispatcher{Pascal}`. The `Node` type, `node!` macro, and
`Dispatcher::node()` / `clone_dispatcher()` methods are removed.

Dispatchers are now always registered at compile time, removing the
`with_dispatcher` / `with_dispatchers` methods and the
`PathfinderConfig` API. The `dispatch_tree` feature now only controls
the matching strategy (trie vs linear list).

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.

std::io::Write import

Replace r_println!/r_print! macro usage across all example renderers
with
explicit RenderResult construction using std::io::Write, enabling more
flexible output handling and reducing reliance on macro-side effects.