Add ability to clean timeline

[onel]

Related to #19

Add ability to clean timeline in WebRTCStats.

• Add clearTimeline method to the WebRTCStats class in src/index.ts to clear the timeline of events.
• Update the destroy method in src/index.ts to call the clearTimeline method, ensuring the timeline is cleared at the end of the session.
• Update README.md to include documentation for the new clearTimeline method in the API section.

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