increase slot observability for 6 second slots

Add more metrics to better understand the cost of each step in the slot

The issue does not name a file, test, or entry point. Start by locating the code that processes six-second slots and the existing metrics around each processing step; compare their coverage and determine which additional measurements are required. Done means the relevant step costs are exposed as metrics and the changes are covered by the project's existing validation.

Written by the indexing model from the issue text.