Fixed INT8 handling, support for testing statements, proper connection error handling

[Hydrocharged]

This primarily implements four things:

1. We now discard all messages until we reach a Sync message when an error occurs, which is consistent with the documentation.
2. Proper support for boolean results. The sqllogictests make use of them, and GMS doesn't have a native boolean type, so we treat all booleans as Int32 types. You can read more in the comments.
3. Proper error handling is the multi-message test case. Our conn.Query calls in tests only return specific kinds of errors, and all other errors are put into the returned rows. This differs from conn.Exec, which returns all errors. Previously, we never checked for an error in rows (since I never knew an error would be put there), so it was getting swallowed. We now properly handle those errors.
4. Expanded statement support for Describe messages. I noticed in the zachmu/err-handling-repro branch that the test file testing/go/prepared_statement_test.go is inconsistent with the general test framework, as it runs the setup statements using conn.Query rather than conn.Execute. We don't support Describe at all right now, as GMS currently requires analyzing a statement to determine the output schema, and analyzing some statements produces execution side effects. As a workaround, we start a transaction, execute the query, record the schema, and rollback the transaction. This does not work for any commands that implicitly commit the transaction, so this adds another hack to fake it by running an equivalent DROP to select CREATE statements. This does cause an implicit commit, but it's better than failing for now.

[zachmu]

LGTM

[zachmu]

I'm gonna merge this, but notes for next round of improvements:

1. Error handling is probably wrong for non-extended query syntax (we'll block waiting for a sync that never comes)
2. The describe solution right now is a hot mess. We can't be execute statements just to get their result set descriptions, we need to expose analyzer capabilities to this layer. Might fix that next.

[Hydrocharged]

It handles non-extended syntax as well, as all of those messages will mark that they are the end.