Fix documentation file to end with newline for POSIX compliance

Co-authored-by: 0xrinegade <[email protected]>

Author: Copilot

docs/developer/error_handling.md

@@ -153,4 +153,4 @@ RUST_LOG=debug cargo run
 4. **Provide meaningful error context** using error builders
 5. **Sanitize sensitive data** before logging
 6. **Use appropriate error types** for categorization
-7. **Test error handling paths** in integration tests
+7. **Test error handling paths** in integration tests