Description:
Introduce code coverage tracking that measures how much of the WT codebase is exercised when running the existing test suite (python, test/format, test/checkpoint), including both existing WT components and newly added Disagg components. The goal is to run the current tests, see which areas of the codebase they actually cover, and use this data to identify gaps and guide future testing. Coverage reporting should run as part of the normal test flow.

Outcome:

• Coverage results are generated for Disagg (utise test/format, python test, test/checkpoint) as we do for classic WT (here).
• Corresponding coverage task added to Evergreen under [Failure Expected] (ARMV9) Amazon 2023 Disagg Stress Tests.