feat: add screencast fps option

[mturac]

Addresses #2291.

Summary

• add an --experimental-screencast-fps option for screencast recording
• validate the value as a positive integer and imply --experimental-screencast
• pass the configured FPS through to Puppeteer's screencast() call
• update generated option docs and flag telemetry metadata

Testing

• git diff --check origin/main...HEAD
• npm run check-format
• npm run typecheck
• npm test -- --test-only tests/tools/screencast.test.ts tests/cli.test.ts

[mturac]

Validation refreshed on the current head:

git diff --check origin/main...HEAD
npm run test -- tests/tools/screencast.test.ts tests/cli.test.ts
npm run check-format

All three passed locally.

[mturac]

Rebased this branch onto the current main and re-ran validation.

Validation:

• git diff --check origin/main...HEAD
• npm run test -- tests/tools/screencast.test.ts tests/cli.test.ts
• npm run check-format

[nattallius]

Thanks for your pr! Since the direction for the linked issue #2291 hasn't been fully confirmed yet, let's hold off on merging or closing it for now. We can keep this on hold until we get definitive confirmation on the final direction