[ie/soundcloud] Fix download format extraction

[bashonly]

The original download formats are now only available when logged in. This patch adds auth headers to the API request for them and warns when the download formats exist but login is required.

Resulting changes:

• The redefined _download_json() was causing problems with error handling, and it's cleaner/more obvious to just define a _call_api() method instead.

• The original download format API call now also counts towards the API rate-limit, so moved the 429 retry loop code into a method so it could be used in multiple places during extraction. EDIT: The original download format API call does not count towards the API rate-limit, so this change was reverted.

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

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

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)

[tntmod54321]

Behaves as expected.
When downloads are available they will succeed or raise a warning depending on whether auth has been passed.

[tntmod54321]

Tested and behaves as expected:
extraction without auth: gives warning
extraction with auth: download format is available and works
extraction with auth while ratelimited: download format still works (expected)