[UR] [L0 v2] Remove event allocation in command buffer

[Xewar313]

Is your feature request related to a problem? Please describe

As proposed in #17709 (comment), the command buffer in L0 adapter v2 should not allocate additional events during enqueue, but use just two events interchangeably.

Describe the solution you would like

No response

Describe alternatives you have considered

No response

Additional context

No response

[igchor]

After some thought, to avoid allocating events, we would have to keep a pre-queue event (not just 2) in the command_buffer, as we cannot reuse events across queues. The benefits of doing it are unclear - we can just as well keep allocating events from the pool. I'm closing this issue for now.