feat: replace events.track() by events.send()

[ferreiro]

Improving our SDKs signature. Track was a bad naming we picked for a backend-focused SDK. once we ship our frontend SDK we might want to start adding "identify", "trackEvent", "trackPage" for a more "events-driven" SDK

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Note

Renames Events API methods to events.send() and events.sendBatch(), adding README docs, examples, tests, and changelog entries.

• Events API:
  • API rename: events.track() → events.send(), events.trackBatch() → events.sendBatch() in src/api/events.ts (JSDoc updated).
  • Tests: New coverage for send() and sendBatch() in src/__tests__/events.test.ts (HTTP interactions mocked).
  • Documentation: Added Events API section with examples in README.md.
  • Examples: New examples/events-usage.ts demonstrating single, batch, and custom deduplication flows.
  • Changelog: Added entries highlighting clearer method names and new examples/documentation.

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