In some cases, I've observed that the existing statement cache can leak memory, since it never clears statements from the cache. This PR adds support for providing alternative implementations of the statement cache & monitoring size in order to handle/discover these potential memory leaks.

Before submitting your PR, check that you've:

• Documented new APIs with Haddock markup
• Added @since declarations to the Haddock
• Ran stylish-haskell on any changed files.
• Adhered to the code style (see the .editorconfig file for details)

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Bumped the version number if there isn't an (unreleased) on the Changelog
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)