handle prepared statement in collisions

[heavycrystal]

As per jackc/pgx#1847, pgx keeps track of prepared statements it creates and expects the connection to be in sync with the cache (because prepared statements are not global, they're per backend). Some poolers like PgBouncer and Supavisor are breaking this assumption and causing multiple executions of the same SQL statement to fail like:

failed to fetch custom type mapping: failed to get customTypeMapping: ERROR: prepared statement "stmtcache_7d186420d84f94f4834117286faada6342a9373d2d7ff41d" already exists

We need to disable automatic prepared statement creation in these cases, or error out gracefully pointing out this is due to poolers