Improve invalid subcommand errors

[AleksZyro]

Fixes #320.

When a command namespace is followed by an invalid subcommand, Cleo now reports the full attempted command instead of only the namespace.

For example, foo baz now reports that foo baz does not exist, rather than saying that foo does not exist.

Tested with:

python -m pytest tests/test_application.py::test_invalid_subcommand_uses_full_command_name -q
python -m pytest tests/test_application.py -q
python -m ruff check src/cleo/application.py tests/test_application.py

[AleksZyro]

Hi! I wanted to follow up on this PR and ask whether the proposed invalid-subcommand error handling is still useful for Cleo. I’m happy to make any changes or add more test coverage if needed. Thanks for reviewing.