Change the default implementation to calculate step stats more efficiently

[prha]

Summary & Motivation

By default, we calculate step stats by fetching all of the events and filtering in-memory to construct the step stat summary.

This PR changes the event fetch to pass in an event type filter.

This has the biggest impact for runs that have a lot of unstructured events and that do not directly inherit from the SqlEventLogStorage (e.g. some Cloud storage implementations)

How I Tested These Changes

BK