Reconcile main-thread-tasks with Long Tasks


Based on this screenshot, you can see RUM long tasks don't line up with RPP 'task's, but those RPP tasks (I believe) are the RunTask events we use to form the basis of our long task stuff.

There's a new 'LongTaskTracker' event under the `scheduler.long_tasks` category. It seems to match the rum definition. I believe we want to migrate to those. still some research required as there's plenty of weirdness in this area.

Start by comparing the RUM long-task definition with the RPP task events shown in the linked screenshot, then investigate the newer LongTaskTracker event under scheduler.long_tasks. Confirm whether it matches the RUM definition and identify the remaining edge cases. Done means the long-task handling is reconciled with the intended event source and the behavior is verified against the observed mismatch.

Written by the indexing model from the issue text.