Migrate state, cli_args, and output out of main.py

[rolandwalker]

Description

Create a mycli/app_state.py, mycli/cli_args.py, and mycli/output.py, factoring logic out of mycli/main.py, with no functional change.

Like other refactors, this could be seen as incomplete in various ways, but it moves us forward on reducing LOC in main.py (which is now a third of the size from before refactoring started).

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[scottnemes]

This seems like it short circuits the mypy checks; was it done to get past errors that were happening? Ran this through Claude and it recommends something like the below instead to prevent future errors not being caught by mypy:

if TYPE_CHECKING:
    from cli_helpers.tabular_output import TabularOutputFormatter
    from configobj import ConfigObj

    class _MyCliState(Protocol):
        # External attributes supplied by the concrete class (MyCli).
        config: ConfigObj
        my_cnf: ConfigObj
        logfile: TextIOWrapper | None
        prompt_session: Any
        prompt_format: str
        prompt_lines: int
        explicit_pager: bool
        ptoolkit_style: Any
        helpers_style: Any
        helpers_warnings_style: Any
        main_formatter: TabularOutputFormatter
        redirect_formatter: TabularOutputFormatter

        # Provided by AppStateMixin.
        def read_my_cnf(self, cnf: ConfigObj, keys: list[str]) -> dict[str, Any]: ...

        # Provided by OutputMixin itself; declared so cross-method calls type-check.
        def log_output(self, output: str | AnyFormattedText) -> None: ...
        def get_output_margin(self, status: str | None = None) -> int: ...
        def get_reserved_space(self) -> int: ...


class OutputMixin:
    def output_timing(self: _MyCliState, timing: str, is_warnings_style: bool = False) -> None:
...

Will approve still in case you do not think that is an issue however.

[rolandwalker]

Thanks! Will try it.