tools: add ClinicalTrials.gov API as function tool

[AidanCooper]

Thank you for contributing to the Cohere Toolkit!

• PR title: "area: description"

Enables clinical studies to be retrieved from ClinicalTrials.gov, with optional filtering by condition, location, intervention, and recruiting status.

• Add tests and docs: Please include testing and documentation for your changes
• Lint and test: Run make lint and make run-tests

Three unrelated tests are failing locally for me:

FAILED src/backend/tests/routers/test_deployment.py::test_list_deployments_has_all_option[mock_available_model_deployments0] - AssertionError: assert 5 == 3
FAILED src/backend/tests/routers/test_deployment.py::test_list_deployments_no_available_models_404[mock_available_model_deployments0] - assert 200 == 404
FAILED src/backend/tests/routers/test_deployment.py::test_list_deployments_no_available_models_with_all_option[mock_available_model_deployments0] - AssertionError: assert 5 == 3

[CLAassistant]

All committers have signed the CLA.

[lusmoura]

Great addition to the toolkit! Thank you for contributing 😄 You might need to update your branch before merging it.

[AidanCooper]

Great addition to the toolkit! Thank you for contributing 😄 You might need to update your branch before merging it.

Thanks! Branch is up to date — just need someone with write access to merge