Previously we set up migrations directly as structs which doesn't match
how users will create them. For the new test framework, we'll instead
write TOML for migrations. This brings the tests closer to how an end
user will interact with Reshape and also lets us write tests to match
the examples in the documentation.
This reduces the amount of boilerplate required to run a test and also
has the added benefit of extending tests as we can now easily test both the
completion and abort paths. So far two tests have been ported over,
create_table and add_column, with the rest to follow.
The framework also improves the output of tests, adding sections clearly
indicating in which part of the migration process a test failed.
This checks for dangling temporary columns, triggers and function which
were used by migrations but should be removed once the migration has
been completed or aborted.
