Refactor/replace httpretty with responses

[kaya70875]

This PR migrates the test suite's HTTP mocking library from httpretty (which is no langer actively maintained) to responses to provide better stability and integration with the requests library. The existing unittest.TestCase architecture was preserved to keep the refactor focused and the diff clean.

Key Changes

• Mock Lifecycle: Replaced httpretty.activate with responses.start() and self.addCleanup(responses.stop) inside setUp() to ensure base mocks persist correctly across the test lifecycle.

• State Overrides: Used responses.replace() and chained responses.add() calls to handle test-specific mock overrides and sequential retry logic (e.g., for proxy and consent cookie tests).

• Content-Type Fixes: Explicitly added content_type="application/json" to innertube API mocks. responses defaults to text/plain, which was preventing the error handler from parsing JSON and causing false-positive VideoUnplayable exceptions.

[coveralls]

Pull Request Test Coverage Report for Build 22795606950

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 21472046532:	0.0%
Covered Lines:	505
Relevant Lines:	505

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💛 - Coveralls

[jdepoix]

Thank you for your contribution @kaya70875 🙏