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