Adds @with_annotated decorator that builds argparse parsers from type-annotated
function signatures. Supports Annotated[T, Argument(...)] / Annotated[T, Option(...)]
metadata, automatic positional/option detection, optional unwrapping, collections,
enums, literals, Path completion, subcommands via subcommand_to=, base_command=True
with cmd2_handler dispatch, and argument/mutually-exclusive groups.

- New module cmd2/annotated.py with Argument, Option, with_annotated, and
  build_parser_from_function helpers
- Comprehensive test suite in tests/test_annotated.py
- Example in examples/annotated_example.py
- Docs updates in docs/features/argument_processing.md

- aliases param: Sequence[str] = () to match as_subcommand_to()
- update aliases None checks now that it defaults to ()
- type with_annotated via @overload (no longer untyped decorator)
- drop experimental annotated exports from cmd2/__init__.py
- import from cmd2.annotated in example/tests/docs; fix example mypy

…rals

Also:
- Fix minor edge case silent failure bug
- Add description of this new feature to CHANGELOG under an "Experimental Features" section for the 4.0.0 release

…ed as the leaf command

If a subcommand is also a `base_command` (e.g., intermediate subcommands), has `subcommand_required=False`, and is executed without any further subcommands provided by the user, it becomes the leaf command. The `cmd_wrapper` of the top-level command will set `ns.cmd2_handler` to point to this nested `handler` itself. Extracting it through `_filtered_namespace_kwargs` and passing it to the command function causes the function to call its own handler repeatedly via `if cmd2_handler: cmd2_handler()`, leading to an infinite recursion (stack overflow).

This commit adds code to detect and short-circuit that potential infinite recursion.

Also: Bump a

Document that this feature works in a manner similar to Typer to help make it more discoverable for users.