[extractor/pbskids] Add support for pbskids.org videos

[snixon]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

This PR adds support for videos on the pbskids.org site. I added it as a second extractor to the existing extractor/pbs.py, but if that's not appropriate I can split it out to its own file, it doesn't share any code with the existing extractor.

I think I found all the proper convenience methods, passes flake8

Fixes #2440

Template

Before submitting a pull request make sure you have:

• 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

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

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

🤖 Generated by Copilot at ec225c9

Summary

🚚🧒📊

Added a new extractor for PBS Kids videos. The PBSKidsIE class in pbs.py handles the JSON data from the PBS Kids website and extracts the video formats and metadata. The class is registered in _extractors.py as a supported extractor.

To support PBS Kids videos
We imported json and traverse_obj modules
And created a new class PBSKidsIE
That parses the data and extracts the info we need
To download and enjoy the shows

Walkthrough

• Add a new extractor class PBSKidsIE to handle PBS Kids videos (link)
• Import json module and traverse_obj function to parse and access JSON data embedded in the webpage (link, link)
• Register PBSKidsIE as a supported extractor in _extractors.py (link)
• Define the URL pattern, test cases, and extraction method for PBSKidsIE (link)
• Extract various metadata fields from the JSON data, such as title, description, duration, series, categories, upload_date, etc. (link)
• Extract the m3u8 playlist URL and call _extract_m3u8_formats_and_subtitles to get the available formats and subtitles (link)
• Return a dictionary with the extracted information (link)

[snixon]

Thanks for the review!

[snixon]

@pukkandan Could you take a look? I've got the changes in place. Would you prefer a cleaner PR with just a single commit?

[Grub4K]

The PR will be squashed upon merge, resulting in a single commit anyways. Do not worry about commit messages and amount of commits