feat: add frame capture and clipboard helper APIs

[shrey150]

Summary

• add Hls.captureFrame(media, type?, quality?) to capture current video frame as an image Blob
• add Hls.copyFrameToClipboard(media, type?, quality?) to write captured frame to Clipboard
• add unit tests for non-video rejection, canvas capture flow, and clipboard write flow

Motivation

Our dashboard player supports pausing and a right-click action to copy the current frame as an image. These helper APIs make this use-case reusable upstream for hls.js consumers.

Testing

• npx eslint src/hls.ts tests/unit/hls.ts
• npm run test:unit -- --grep "static frame helpers"

Notes

• Clipboard image writes are subject to browser permission/user-gesture constraints.

[robwalch]

Thank you for contributing a PR to HLS.js.

This is not a feature related to streaming HLS or supporting MSE based playback. As such it is not something we'll be willing to take at this time.