fix: improve thread safety in CrowdinLocalizationDownloader completion handling

[serhii-londar]

• Added locking mechanism to safely read accumulated state (strings, plurals, errors) when no files are available for download.
• Ensured completion handler returns the correct state without risking data corruption during concurrent access.

[codecov]

Codecov Report

❌ Patch coverage is 46.15385% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.17%. Comparing base (87517b4) to head (be191c4).

Files with missing lines	Patch %	Lines
...tionDownloader/CrowdinLocalizationDownloader.swift	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #346      +/-   ##
==========================================
+ Coverage   62.72%   63.17%   +0.45%     
==========================================
  Files         126      126              
  Lines        4839     4851      +12     
==========================================
+ Hits         3035     3064      +29     
+ Misses       1804     1787      -17     

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[Copilot]

Pull Request Overview

This PR enhances thread safety in the CrowdinLocalizationDownloader by adding proper locking when reading accumulated state in the no-files-to-download scenario. It also improves test isolation by adding comprehensive state cleanup in test setup.

• Added lock/unlock mechanism to safely capture strings, plurals, and errors before invoking completion handler
• Enhanced test setup with global state cleanup to prevent test interference

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Sources/CrowdinSDK/Providers/Crowdin/LocalizationDownloader/CrowdinLocalizationDownloader.swift	Added thread-safe state reading with lock mechanism when no files are available for download
Sources/Tests/Core/RealLocalizationProviderTests.swift	Added global state cleanup in setUp() and manifestManager.clear() call to improve test isolation

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[Copilot]

The lock is not released if an exception occurs between lock() and unlock(). Consider using defer to ensure the lock is always unlocked, even in exceptional cases: self.lock.lock(); defer { self.lock.unlock() }