Add final modifier to classes not designed for extension (#44)

[s2x]

Summary

• Add final modifier to SymfonyController, StaticFilesMiddleware, and RequestConverter
• These classes are not designed for extension

Closes #44

[s2x]

Code Review: Additional Classes Not Marked as final

I reviewed the current PR changes and compared them against the rest of the codebase. The 3 classes in this PR are correctly marked as final. ✅

However, there are 3 additional classes that could also be marked as final but were left untouched:

Safe to mark as final:

• src/Reboot/Strategy/MemoryRebootStrategy.php — implements interface, no subclasses
• src/Command/WorkermanCommand.php — extends Symfony Command, not designed for extension
• src/Exception/NoResponseStrategyException.php — extends \LogicException, no subclasses

Not recommended to mark as final:

• src/Http/Request.php — extends Workerman Request, may be extended by users
• src/Runtime.php — extends SymfonyRuntime, commonly extended for custom runtime behavior
• src/Protocol/Http/Response/StreamedBinaryFileResponse.php — extends Symfony BinaryFileResponse, may be extended

Suggestion

Consider adding final to the 3 safe classes above for consistency. Would you like me to push a follow-up commit?