[exa-js]: add effort param for deep search type

[devin-ai-integration]

Summary

Adds an optional effort parameter to the DeepSearchOptions type for deep search. This allows users to configure the effort level when using type: "deep":

• "medium" (default): Faster, cheaper searches using deep_lite service
• "high": Maximum quality using full deep service

This corresponds to the backend change in exa-labs/monorepo#11290.

Review & Testing Checklist for Human

• Verify the param name effort matches the backend API expectation (check if camelCase conversion is needed)
• Test a deep search call with effort: "high" against the API to confirm it's accepted

Notes

Requested by: William Li ([email protected])
Link to Devin run: https://app.devin.ai/sessions/6c21ac37bc6f4dbf8c37d31f7fbbc388

A corresponding PR was also created for exa-py to add the same parameter.

[devin-ai-integration]

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