Function create_test_context 

pub fn create_test_context() -> KernelContext

Create a KernelContext with a real in-memory buffer manager.

This is the standard test context used across all modules. It provides:

• Real TestBufferManager (stores and retrieves buffers)
• Fresh EventBus
• Default MotionEngine, TextObjectEngine
• Empty MarkBank, OptionRegistry, ServiceRegistry

For tests that need services (undo, search, etc.), create a context with this function and then register services on ctx.services.