Tyro

Fix spacing bug.

Support general mappings, improve helptext.

Type inference improvements:
- Support `typing.Any` in type narrowing logic.
- Fix bug preventing contained types from being inferred when `dict` is used instead of `dict[KT, VT]`.

Fixes for subparsers:
- Removed obsolete logic that equated optional types (with `Optional[T]` or `Union[T, None]`) as not required (when a default is provided).
- Fix corner case for subparsers in nested classes.

Minor Poetry fixes.

New features:
- Support for mixed-type literals.
- Support nesting structures in standard Python containers: `List[Struct]`, `Set[Struct]`, `Tuple[Struct, Struct]`, `Dict[str, Struct]`, etc.
- Add `dcargs.generate_parser()` for integration with tools like `shtab`, `argcomplete`, `pyzshcomplete`, etc.
- Support defaults with narrower types than annotations.
- Support for including multiple optional subparsers, more clear/verbose subcommand names.
- Support inheritance from generic types.
- Generalized support for directly passing in types, eg `dcargs.cli(Union[SubcommandA, SubcommandB])`.

Maintenance:
- Helptext formatting improvements: consistency for subcommands, Windows support, edge case fixes.
- Reduce redundant logic.