[ITV] Update ITV extractor from yt-dlp back-port

[dirkf]

Please follow the guide below

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Before submitting a pull request make sure you have:

• Searched the bugtracker for similar pull requests
• Read adding new extractor tutorial
• Read youtube-dl coding conventions and adjusted the code to meet them
• Covered the code with tests (note that PRs without tests will be REJECTED)
• Checked the code with flake8

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense, except where
• I am not the original author of this code but it is in public domain or released under Unlicense (yt-dlp/yt_dlp/extractor/itv.py)

What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

This PR back-ports the ITV extractor from yt-dlp, so incorporating all the latest fixes and facilitating future joint updates.

The PR from #28955 is included for the record as an an interim commit.

In addition the following changes are applied:

• work-around for ITV using : as a decimal point in duration value
• set default UA for extraction as Mozilla/5.0 to avoid read time-out in extraction
• ditto for download to avoid 403
• detect and handle 404 error for Episode not found and We're really sorry.

Resolves #25796.
Resolves #27582.
Resolves #28906.
Resolves #29620.
Resolves #30265.
Resolves #30578.
Resolves #30994.

Closes #28955.

Now updated for ITVX instead/as well.

Resolves #31363.

Also updated ITV BTCC, handles news articles.

Supersedes, closes #25254.

[stsquad]

I just want to confirm that testing this branch I was able to download what I was looking to where the current upstream master would just timeout and fail.

[MysticMerlin]

Hi,
I'm not a complete novice but I'm having some difficulty following what's going on & whether the problem with the ITVX has been fixed. I can see that dirkf has been very busy & I'h sure there are many thousands of people appreciating all his efforts & anybody else that is capable of contributing. I'm afraid I don't have the experience or knowledge to offer any contribution from my side. So, in layman's terms where are we at as regards ITVX? Thanks.

[dirkf]

The updated extractor is now in the git master repository code that would be used to make a release. A release built from git master should support ITVX. Also, installing from the git master with pip should do so.