Introduce wait queues for blocking kernel tasks #185

Summary

Provide a reusable wait-queue primitive so tasks can sleep until a condition or event becomes available instead of repeatedly polling.

Scope

• Define enqueue, wake-one, wake-all, and cancellation semantics.
• Prevent lost wakeups when a condition changes while a task is preparing to sleep.
• Specify lock ordering and the interaction with scheduler run queues.
• Keep the primitive independent of specific devices or syscall implementations.

Acceptance criteria

• Host tests cover empty queues, multiple waiters, wake-one, wake-all, and repeated enqueue/dequeue.
• Tests or a deterministic model cover the condition-check/sleep race.
• Woken tasks become runnable exactly once.
• Document interrupt-context restrictions and locking invariants.

Engineering constraints

• Keep the kernel Rust-first, no_std, and x86_64-compatible.
• Integrate with existing Rustalis subsystem interfaces; do not create a parallel implementation.
• Document ownership, initialization order, failure behavior, and any architecture-specific unsafe invariants.
• Add host-side tests for hardware-independent logic and QEMU coverage for hardware paths where practical.
• Do not claim verification that has not actually been run.