fix: update unit tests to require live Crowdin distribution for execution

[serhii-londar]

Note

Locks live-dependent unit tests behind an environment flag and stabilizes CI test execution.

• Gate multiple XCTest classes with setUpWithError + XCTSkipUnless(ProcessInfo... ["CROWDIN_LIVE_TESTS"] == "1") to skip tests unless a live distribution is enabled
• Disable Xcode parallel test execution by adding -parallel-testing-enabled NO in .github/workflows/build.yml
• Improve test reliability by fulfilling expectations on error paths in CrowdinSupportedLanguagesThreadSafetyTests and ensuring proper SDK cleanup in tearDown

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[andrii-bodnar]

@serhii-londar as I understand it, these tests will only execute locally when CROWDIN_LIVE_TESTS is enabled. I'm concerned about the reliability of such tests. We can't control whether everyone will run them locally, so they could become outdated or broken without our knowledge.

I would suggest improving the tests environment by mocking the distribution of creating some test distribution.

[serhii-londar]

@andrii-bodnar We have test distribution and test currently using it. I wanted to make tests more stable, by disabling live tests for now. I suggest closing this request and disabling parallel tests execution in #363. Let's check whether it will help at this point.