[UR][L0] fix event lifetime associated with async free (#21325)
A recent patch #21320, changed how events are allocated for async
allocations. Instead of always allocating an event, we now allocate it
optionally, depending on whether user specified it. But that changed did
not update how event refcounts are updated, in the case that the event
is actually allocated. This could lead to potential use-after-free.
This patch moves the refcount management into command list manager, and
correctly increments it when required.
