feat: Expose underlying cache_db with env.db() function

[jbargu]

Give an overview of the tasks completed
Expose underlying cache_db with env.db() function. This is useful to check the execution state and environment re-creation without stopping the simulation.

Link to issue(s) that this PR closes

REMINDER! Please check that you have done the following prior to submitting this PR:

• Checked that the relevant version(s) have been incremented if necessary.
  • please advise if version is to be incremented
• Ran both and made any changes necessary for:
  • cargo +nightly fmt --all
  • cargo clippy --all

You can install the nightly toolchain on your system by:

rustup toolchain install nightly

[Alexangelj]

Reviewing this next week with the team