[roll] Roll fuchsia [kernel][tracing] Fix duplicate flow IDs in futex, pager, and IPC

Resolve flow_duplicate_id errors in Perfetto trace processing by
ensuring all kernel-emitted flow begin events are properly balanced or
uniquely correlated:

1. Futex Contention (futex_context.cc):
   Emit LOCK_TRACE_FLOW_END in FutexWait's non-OK cleanup path (e.g.
   timeout, suspension, or interruption) so contention flows do not
   remain perpetually active in the trace processor.
2. Pager Requests (pager_proxy.cc, pager_proxy.h):
   Use flow_id_generate() instead of casting &packet_ to uintptr_t.
   Because packet_ is a member variable reused across consecutive
   requests, pointer recycling caused duplicate flow begin collisions
   if a previous flow was cancelled or lost.
3. Channel IPC (channel_dispatcher.cc):
   Use the message packet pointer address for ChannelMessageFlowId
   when txid is not kernel-generated (!IsKernelGeneratedTxid), rather
   than only when txid == 0. This prevents backlog collisions when
   userspace clients queue multiple requests with non-zero txids.

Original-Original-Fixed: 545311368
Test: fx test futex-ownership-test
Test: Captured trace and verified 0 kernel flow_duplicate_id errors
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1769097
Original-Original-Revision: 858b7a62af107a3e41bcce3c1b3ab783b9fe7a88
GitOrigin-RevId: 728f37d1eefc40e22210cdd7cb414e6bdad278c6
Change-Id: I4c434a9b4b028e873180d5c451c936b448dfa12f