Run CREATE SCHEMA, CREATE TABLE and CREATE INDEX in a session

[tamnd]

Part of #3.

A session now runs CREATE SCHEMA, CREATE TABLE and CREATE INDEX. Before this change they gave 0A000. The analyzer part came in #174.

What changes

• New rupg_session::store::Store. It holds the catalog of the last commit, which all the sessions of a server share. The server makes one store and gives it to each session.
• A statement that defines an object takes the lock of the store. The transaction holds the lock until it ends, so only one transaction at a time changes the catalog. Another session that defines an object waits for the lock, and a cancel stops the wait with 57014. While it waits it lets the other tasks run, so the simulated scheduler, which runs all the tasks on one thread, does not stop.
• At COMMIT the copy of the transaction becomes the catalog of the last commit. At a rollback the changes go, but the OIDs that the transaction used stay used, as in PostgreSQL.
• When a statement fails, its changes go at once. The statements before it in the same transaction keep their changes until the transaction ends.
• The warnings and notices of a definition go to the client before the result, as NoticeResponse.
• search_path, current_schemas and the analyzer now find the schemas of the catalog, not only pg_catalog, pg_toast and public.
• The extended protocol runs a definition at Execute, as PostgreSQL does. Parse does not refuse it.

Test

• The new session test runs the same statements as a script on the PostgreSQL 19 oracle and expects the same tags, errors, notices and positions. It covers a rollback, a failed block, IF NOT EXISTS, the extended protocol and a second session that sees the committed catalog.
• Three tests of the store check that a rollback keeps the OIDs used, that a cancel stops the wait for the lock, and that a session that waits lets the holder of the lock run.
• srvtest passed on server1.