run SPT in parallel, and split annotation allocator

Summary:
This diff includes two main changes:
1) When creating an annotation, a dedicated annotation allocator can be used, instead of the default allocator. This allows some annotation to be deallocated  right after the end of their usage completely. Furthermore, having the ability to use dedicated allocators allows running SPT in parallel where each task uses a different allocator.

2) SPT is parallelized.

(cherry picked from FBD15913492)