Adds a method get the underlying sqlite3 pointer

[agentsim]

Per #430, adds a method as_raw_handle() to get the underlying sqlite3* from a SqliteConnection.

This PR is cleaner (a single commit). The previous PR also failed CI due to a (hopefully) random fault in docker.

[mehcode]

failed CI due to a (hopefully) random fault in docker.

GitHub Actions is randomly failing to run docker-compose run .... It looks like a potential race condition with it starting the docker daemon? Not sure.

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The PR looks good to me except.. I think we should require &mut self as you're returning a *mut sqlite3 there. Thoughts?

[agentsim]

I left it as &self since as_ptr() on ConnectionHandle takes &self and I assumed there was a reason for that.

[abonander]

I believe it's an antipattern to have a method take &self and return *mut Foo. It looks like SqliteConnectionHandle::as_ptr() can be changed to take &mut self and all usages of it should still compile.

It's especially important to take &mut self for the public API, I think, as we probably want to enforce that the connection isn't currently being used.

[abonander]

I feel like we need to list some do-s and don't-s for this pointer but I'm not sure what those should be.

[agentsim]

The obvious two that come to mind are not to close the connection or free the pointer. I don't think the Rust docs in the standard library for similar low-level things spell out the do-s and don't-s.

[mehcode]

Thanks for the addition. We can always improve docs as we move along. Maybe just a general warning like "preserve the pointer and don't close the connection or bad things will happen".