fix: undefined / null serialization

[schiller-manuel]

fixes #5416

Summary by CodeRabbit

• New Features

  • Added primitives route for testing server function capabilities.

• Improvements

  • Enhanced server function request and response handling with improved payload serialization.
  • Added SSR query integration support for better server-side rendering performance.
  • Improved error logging and request validation for server functions.

• Tests

  • Added comprehensive end-to-end tests for server function primitives.