Add a `From<pack_Type> for crate::Entry` implementation in
`dispatcher!()` macro and a default `Entry` pack type in
`gen_program!()` for ergonomic program entry handling

Move pathf type resolution from `program_final_gen` to `gen_program` and
isolate generated code inside `__this_program_impl` to prevent namespace
pollution

Add a new `#[command]` attribute macro (feature-gated behind
`extra_macros`) that converts a plain function with a `Vec<String>`
parameter into a fully wired Mingling command. The macro generates a
`dispatcher!` call, a `#[chain]` wrapper, and a hidden module
re-exporting
all generated types.

Also add `CommandPattern` to the pathf pattern analyzer to recognize
`#[command]`-annotated functions and track their generated hidden
modules.

Add `unwrap_or_default`, `unwrap_or_else`, and `expect` methods to
reduce boilerplate when working with parsed argument tuples

Add `FilePath`, `NoFilePath`, `DirPath`, `NoDirPath`, `SymlinkPath`,
`NoSymlinkPath`, `NoPath`, and `RecursiveFiles` wrapper types with
filesystem validation at parse time. Each type implements
`SinglePickable`
and provides standard conversions via `From`, `AsRef`, `Deref`, and
`DerefMut`.