Implement semaphore synchronization primitive

[pbalduino]

Goal

Implement counting semaphores for kernel synchronization and resource management.

Context

Semaphores are essential synchronization primitives that allow controlling access to a finite number of resources. They're particularly useful for producer-consumer scenarios, resource pools, and implementing other synchronization constructs.

Definition of Done

• Core functionality: Implement ksem_init(), ksem_wait(), ksem_post(), ksem_destroy()
• Counting semaphore: Support for initial count and maximum count values
• Timeout support: Add ksem_wait_timeout() for non-blocking waits with timeout
• Try operations: Implement ksem_trywait() for non-blocking attempts
• Error handling: Proper error codes and validation for all operations
• Thread safety: Ensure all operations are atomic and thread-safe
• Performance: Optimize for minimal overhead in common use cases
• Integration: Work seamlessly with kernel scheduler and thread management

Use Cases

• Resource pool management (memory pools, connection pools)
• Producer-consumer synchronization
• Rate limiting and flow control
• Barrier implementation
• Building higher-level synchronization primitives