Tyro

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.

Re-add the `py.typed` marker, which was inadvertently deleted.

- Documentation refactor.
- Serialization utilities have been moved to `dcargs.extras.*`.

- Supporting using built-ins directly: `dcargs.cli(int)`, `dcargs.cli(List[str])`, etc.

- Support for nesting collections. (tuples inside tuples inside dictionaries, etc)
- Overhaul mechanisms for handling `Union` types, which are now supported recursively and much more generally (eg `Union[int, str]`, `Union[Tuple[int, int], Tuple[str, str]]`, etc).
- Support `total=False` for `TypedDict` types.
- Helptext generation improvements: conciseness, ignoring ANSI codes when wrapping.
- Add `prog=` argument to `dcargs.cli()`.
- Various minor stability improvements.