Fix zsh completion for namespaced commands

[itscloud0]

Summary

• complete namespaced zsh commands one token at a time instead of inserting escaped spaces
• resolve command options using the full namespaced command path
• add a regression test and news fragment for the zsh completion behavior

Fixes #153

Testing

• uv run --python 3.12 --with pytest --with pytest-mock pytest tests/commands/completion/test_completions_command.py tests/commands/test_command.py -q
• uv run --python 3.12 --with ruff ruff check src/cleo/commands/completions_command.py src/cleo/commands/completions/templates.py tests/commands/completion/test_completions_command.py
• uv run --python 3.12 --with ruff ruff format --check src/cleo/commands/completions_command.py src/cleo/commands/completions/templates.py tests/commands/completion/test_completions_command.py