🧹 Replace debug print with logger in NetworkService

[LeanBitLab]

🎯 What: Replaced print with dart:developer log in NetworkService.
💡 Why: print statements clutter the console and lack metadata (severity, origin). dart:developer log allows for proper filtering by name, passing errors cleanly, and integrating better with development tools.
✅ Verification: Ran flutter analyze and verified network_service_test.dart passes. Checked to make sure pubspec.lock was restored and not accidentally committed.
✨ Result: Improved maintainability and debugging capability in NetworkService without altering application logic.

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PR created automatically by Jules for task 6215276889315686056 started by @LeanBitLab

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