feat: add subcommand support

[arily]

Describe your changes

• add subcommand supports.
• backwards compatible with old commands.
• provided command-pretty-print util.

Related Issues / Projects

usage in production:
https://github.com/ppy-sb/bancho.py/blob/akat-0302-rebased-remove-query-builder/app/sb/streamer_commands.py

# top level command
streamer_commands = CommandSet("streamer", "Streamer commands.")

# register sub command
streamer_list_commands = streamer_commands.subcommand(
    CommandSet(
        "list", # subcommand keyword, "!streamer list" in this case
        "manage streamer list.",
    )
)

# register handlers like normal
@streamer_commands.add(Privileges.VERIFIED, aliases=["", "h"])
async def streamer_help(ctx: Context) -> str | None:
    """Show this message."""

    # provided help_pure will pretty-print commands as well as sub commands,
    # I'm open for better naming
    return help_pure(
        ctx,
        [*streamer_commands.commands, *streamer_commands.subcommands],
        app.settings.COMMAND_PREFIX + "streamer",
    )

# register subcommands
@streamer_list_commands.add(Privileges.DEVELOPER, aliases=["", "h"])
@streamer_list_commands.add(Privileges.MODERATOR, aliases=["", "h"])
@streamer_list_commands.add(Privileges.ADMINISTRATOR, aliases=["", "h"])
async def streamer_list_help(ctx: Context) -> str | None:
    """Show this message."""
    return help_pure(
        ctx,
        [*streamer_list_commands.commands, *streamer_list_commands.subcommands],
        app.settings.COMMAND_PREFIX + "streamer list",
    )

both commands can now be used in-game:

2024-12-11 10:49 arily: !streamer
2024-12-11 10:49 ChinoBot: !streamer help: Show this message.
!streamer list: manage streamer list.
2024-12-11 10:49 arily: !streamer list
2024-12-11 10:49 ChinoBot: !streamer list help: Show this message.

Checklist

• I've manually tested my code