Add gated tool tests for CrewAI and LlamaIndex

[tamerbak]

Summary

CrewAI and LlamaIndex were documented as compatible with gate(), but lacked integration tests.

This PR adds coverage for both frameworks to verify that:

• Gated tools preserve argument properties and required fields.
• Allowed calls execute the underlying function.
• Blocked calls return the configured on_block message without executing the function.

The tests use pytest.importorskip for optional dependencies. Documentation includes usage examples and the tested versions: CrewAI 1.15.22 and llama-index-core 0.14.25.

Validation

• New integration tests: 2 passed.
• Integration test file: 6 passed, 7 skipped because unrelated optional frameworks were not installed.
• Ruff lint and formatting checks passed.
• Prose check passed.

Closes #11