R1:f1a588c771f6

Add a basic profiler to Herald transcripts

Summary:
Ref T13298. Add a simple profiler as a starting point to catch any egregiously expensive rules or conditions.

This doesn't profile rule actions, so if "Add subscriber" (or whatever) is outrageously expensive it won't show up on the profile. Right now, actions get evaluated inside the Adapter so they're hard to profile. A future change could likely dig them out without too much trouble. I generally expect actions to be less expensive than conditions.