fix: update PHP SDK code style to fix failing workflow

[devin-ai-integration]

Fix PHP SDK Code Style Issues

This PR fixes the code style issues in the PHP SDK that were causing the workflow to fail. The changes include:

1. Renamed the httpClient property to _httpClient in LingoDotDevEngine.php
2. Renamed private methods to have an underscore prefix (_localizeChunk, _extractPayloadChunks, _countWordsInRecord, _createId)
3. Updated references to these methods throughout the file
4. Fixed doc comments by separating @return tags from parameter tags
5. Updated the LingoDotDevEngineTest.php file to reference the renamed _httpClient property

Link to Devin run

https://app.devin.ai/sessions/0c1c7a8ae9604c4fa3877933f51b7c61

Requested by

Max Prilutskiy (max@lingo.dev)

[devin-ai-integration]

🤖 Devin AI Engineer

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