fix(plugin): support ytAtN attestation format for initial attestation extraction

[Copilot]

YouTube changed its webpage attestation embedding from a direct string assignment (window.ytAtR) to a function call (window.ytAtN), breaking initial attestation extraction entirely.

Changes

• plugin/yt_dlp_plugins/extractor/getpot_bgutil.py: Rewrites _get_attestation to try the new window.ytAtN(...) format first (extracting R property), falling back to the legacy window.ytAtR = ... format
• Plugin version: 1.2.2 → 1.3.0
• CHANGELOG.md: Documents the fix

Format comparison

// Legacy format (ytAtR)
window.ytAtR = '{"bgChallenge": {...}}';

// New format (ytAtN) — challenge is nested under R property
window.ytAtN({..., R: '{"bgChallenge": {...}}', ...});

Ports Brainicism/bgutil-ytdlp-pot-provider#195.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Failed to extract initial attestation from the webpage</issue_title>
<issue_description>Seemingly addressed in this pull?</issue_description>

<agent_instructions>Get Brainicism#195 content and implement it into our project. Also do a research explaning the root cause</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Failed to extract initial attestation from the webpage #103

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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