Add convenience wrapper for pragma optimize

[alexcwatt]

The SQLite docs recommend some cases where PRAGMA optimize; should be used: https://www.sqlite.org/pragma.html#pragma_optimize

I have discovered recently a case where this helped a project at work (https://twitter.com/alexcwatt/status/1851094243323912631) and now I'm wondering about how to make this easier to discover and use.

Do we want a way to test that these wrappers translate to the expected execute call? I wasn't sure what tests to write for this change.

[flavorjones]

@alexcwatt Thanks for this! The omission was mentioned by @rickhull in #559

If we're going to allow the optimize bits to be passed in by the caller, I'd like the API to be a bit more developer-friendly. Would you consider defining some constants in lib/sqlite3/constants.rb?

Our test coverage is pretty bad right now for the pragma methods, so as long as we keep the implementation simple, I think it's probably OK to not have test coverage (or to use a mock to test that the method calls what it should).

[flavorjones]

I'd like to see these bits made available as constants like many of the other sqlite bitmasks in lib/sqlite3/constants.rb

[alexcwatt]

That's a good idea. I took a pass at this; please let me know what you think.

[flavorjones]

Looks good! I added a DEFAULT constant and some tests.

[flavorjones]

And I rebased off origin/main.