[nrk] add support for podcast episodes (closes #27634)

[barsnick]

No support for complete series yet.

Signed-off-by: Moritz Barsnick barsnick@gmx.net

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What is the purpose of your pull request?

• Bug fix
• Improvement
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• New feature

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Description of your pull request and other information

This adds support of NRK podcasts to the [nrk] extractor. It does not support series yet, only single episodes.

It has worked fine for me for the last eight weeks, on various podcasts.

Implementation notes:

• transform_source=js_to_json prevent python for choking on special characters in the JSON embedded in webpages.
• .strip() is required, as one of the tests actually otherwise delivers a title with leading whitespace.
• I wasn't able to get a thumbnail for one of the tests, therefore the thumbnail metadata code has an or None.

[barsnick]

I pushed an additional commit for the flake8 errors in CI. Sorry, I missed them before.

[dstftw]

1. Read coding conventions.
2. This must use existing extractor working with playback end point.