[SYCL][Graph] Optimize graph enqueue for in-order queues

[fabiomestre]

Optimizes the enqueue() function of sycl graphs to bypass the scheduler whenever possible and avoid creating events when not needed.

• Refactors the executable graph enqueue() to have different paths depending on workload:
  • The direct path will be used when there are no host-tasks or accessor requirements in the graph and the execution dependencies are considered safe to bypass the scheduler.
  • The scheduler path will be used when there are requirements in the graph but no host-tasks or, if the execution dependencies require using the scheduler.
  • The multiple partitions path will be used when the graph contains host-tasks which requires scheduling multiple graph partitions. The implementation was also changed to avoid adding unnecessary event dependencies to partition executions and avoiding copying CGData when possible.
• Extends the changes in [SYCL] Do not store last event for in-order queues #18277 to sycl graphs. This means that no implicit events will be created when using in-order queues and graphs without host-tasks. Also updates the handler to only request events from the graph enqueue() when they are needed.

[fabiomestre]

@intel/llvm-gatekeepers Can this PR be merged? The existing failures seem to be CI issues. This PR was green for those jobs before:

Intel-Arc jobs:

• https://github.com/intel/llvm/actions/runs/15681443933/job/44175220366?pr=18792

• https://github.com/intel/llvm/actions/runs/15681443933/job/44175220336?pr=18792

Cuda UR Job:

• https://github.com/intel/llvm/actions/runs/15681443929/job/44174565853?pr=18792

There were only unrelated changes to the HIP UR adapter made since then.

Edit: Nevermind, recently merged commits broke this PR, needs to be rebased.

[fabiomestre]

@intel/llvm-gatekeepers This PR is ready to merge. The CI failure on PVC is unrelated (I have seen it in other PR's).

[uditagarwal97]

@intel/llvm-gatekeepers This PR is ready to merge. The CI failure on PVC is unrelated (I have seen it in other PR's).

Failing tests are unrelated and tracked by #18932