KeyguardRemotePreviewManager: Drop usages of runBlocking

- This CL removes the use of runBlocking from
  KeyguardRemotePreviewManager - previewFactory.create(request) is not
  a suspend function and does not need to be bridged into the context
  with a runBlocking block.
- To maintain performance tracing, a traceSection block is used instead.

Bug: 423462317
Flag: com.android.systemui.do_not_use_run_blocking
Test: atest KeyguardRemotePreviewManagerTest
Change-Id: I94af28a174862d1c2a90b7776d3d39358428340a