Add 'instant' to search type options for lowest latency search

[devin-ai-integration]

Summary

Adds "instant" to the NonDeepSearchOptions type union, enabling users to specify type: "instant" for lowest latency search optimized for real-time applications like autocomplete.

This is a type-only change - no runtime behavior is modified.

Review & Testing Checklist for Human

• Verify backend support: Confirm the Exa API accepts type: "instant" and returns results as expected
• Coordinate releases: This should be released alongside the corresponding exa-py SDK update and docs update

Recommended test plan:

const exa = new Exa('YOUR_API_KEY');
const results = await exa.search('test query', { type: 'instant' });
console.log(results);

Notes

• Related PRs: exa-py SDK update, docs repo update (PR Remove Find Similar and Research from README, update highlights usage #150)
• Requested by: Yi Yang
• Devin session: https://app.devin.ai/sessions/07d4f4bd22314ae6b62875385cd295a2

[devin-ai-integration]

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