Implement Pipes from Scratch: Circular Buffer with Blocking Read/Write

Implement pipe with circular buffer and blocking semantics.

Requirements:

• Define pipe structure with circular buffer and metadata
• Implement pipe_create() to initialize pipe
• Implement pipe_read() to read from pipe (blocks if empty)
• Implement pipe_write() to write to pipe (blocks if full)
• Implement pipe_close() to close read or write end
• Handle EOF when no writers
• Handle broken pipe when no readers
• Use circular buffer logic for read/write positions
• Block using condition variables or simple busy-wait
• Demonstrate parent-child communication
• Show buffer state during operations