Add SQLite session extension

[rodydavis]

This adds support for the SQLite session extension.

• Added build flag
• Added tests

[andrei-goverdovskii]

For whatever it's worth, I'm seeing segfaults trying to apply inapplicable changesets, for example applying a changeset twice:

changeset = new - old
update = old + changeset ✅
update = update + changeset ❌