[extractor/rozhlas] Add MujRozhlas extractor

[stanoarn]

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Description of your pull request and other information

This PR refactors some code from the old RozhlasVltavaIE. This is mainly done so that some of its code can be reused for a new MujRozhlasIE. This new extractor allows for the extraction of data from mujrozhlas.cz. While the data is mostly extractable with the old extractor, the new one is able fetch some addition information (e.g. upload dates) and also works on a different website. The underlying API is the same, but I haven't been able to figure out a way to unify the extraction process.

Fixes #

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

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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

🎧🇨🇿🛠️

Add support for mujrozhlas.cz, a Czech radio website, and improve the existing extractor for rozhlas.cz. Refactor rozhlas.py to share common code and logic between the two extractors. Enhance the error handling and audio format extraction for both sites.

To extract from a Czech radio site
We added a class called MujRozhlasIE
And we tweaked rozhlas.py
To handle errors and formats more sly
Now both extractors work well and are tight

Walkthrough

• Add MujRozhlasIE extractor to handle mujrozhlas.cz URLs (link, link)
• Refactor _extract_video method of RozhlasVltavaIE to extract audio formats (link)
• Add missing imports to rozhlas.py (link)

[bashonly]

@stanoarn Test my changes and let me know what you think

[stanoarn]

Sorry, I was busy with real life stuff, thank you for doing all the hard work. I've added comments explaining which kind of extraction is being tested, and replaced the test for serials, since the one we had been testing has since been removed. Everything else looks alright.