PHP 8.3 update + full module refactor

[SamueleMartini]

Summary

• Added declare(strict_types=1) to all PHP files
• Guard clauses and lazy computation throughout the module
• Deduplicated store filtering logic via getEnabledStores(callable)
• Fixed critical bug: translateParsedContent() param typed string but receives array|string
• Removed dead dependencies, unused imports, redundant annotations
• Specific exception catching (NoSuchEntityException instead of generic Exception)
• Functional style: array_map/array_filter, arrow functions, spaceship operator
• Fixed typos and added previous exception chaining

Test plan

• Verify product translation works (text + Page Builder attributes)
• Verify category translation works
• Verify CMS page/block translation works
• Verify select attribute translation via cron
• Verify admin translate buttons appear and function correctly
• Verify all translation engines (DeepL, OpenAI, Gemini) still work