fix: Update piapro tests and content url scheme

[FinnRG]

Description of your pull request and other information

• Update current piapro tests to finish successfully
• Added the /content url scheme. Every song entry has two urls (i.e. https://piapro.jp/content/hcw0z3a169wtemz6 and https://piapro.jp/t/9cSd) . I've added the /content scheme to _VALID_URL.

Fixes #

Template

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• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

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What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

Copilot Summary

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Summary

🆕🛠📝

Improve piapro extractor functionality and tests. Support new URL formats, add more metadata fields, and update test cases for piapro.py.

piapro extracts
more URLs and info fields
autumn of updates

Walkthrough

• Update _VALID_URL regex to match both /t/ and /content/ URLs for piapro.jp (link)
• Extract more info fields from the webpage, such as description, duration, timestamp, upload_date, view_count, and thumbnail using _html_search_regex and _parse_json methods (link, link)
• Update md5 checksum and add cookies field for the first test case in yt_dlp/extractor/piapro.py (link)