Why this change?
This patch has been added to address the problems identified in https://github.com/rails/rails/issues/35311. For every,
new connection created using the PostgreSQL adapter, 3 queries are executed to fetch type map information from the `pg_type`
system catalog, adding about 1ms overhead to every connection creation.
On multisite clusters where connections are reaped more aggressively, the 3 queries executed
accounts for a significant portion of CPU usage on the PostgreSQL cluster. This patch works around the problem by
caching the type map in a class level attribute to reuse across connections.
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