Schema and catalog introspection over JDBC `DatabaseMetaData`, returning
normalized Clojure data. Each function takes a db spec or datasource (anything
`next.jdbc/get-connection` accepts) and, optionally, a table name.

Table and schema names are accepted as strings or keywords. Results use
keyword names so they compose with the rest of psql-clj.

Operational controls exposed by pgjdbc's `PGConnection` and the JDBC
connection: the backend process id, query cancellation, server parameter
statuses, the default fetch size, the transaction autosave mode, and a helper
to set the per-session statement timeout.

Each function accepts a `java.sql.Connection` (the value `next.jdbc` hands you
inside `with-open`/`on-connection`) and unwraps the pgjdbc `PGConnection` as
needed.

PostgreSQL COPY helpers that use pgjdbc's CopyManager.

COPY runs on a java.sql.Connection. The caller owns the connection and must keep it open for the COPY operation.

Use PostgreSQL from Clojure with connection parameter defaults from PGDATABASE, PGHOST, PGPORT, and PGUSER.
Read the password from ~/.pgpass when it is available.

PostgreSQL LISTEN/NOTIFY helpers that use pgjdbc.

Use a dedicated open connection for listening. pgjdbc surfaces notifications
only when a query is sent or get-notifications is called. A blocking poll
prevents other statements from using the connection until the poll returns.

Match ~/.pgpass passwords to db specs.

Hikari connection pool.

Resolve pgjdbc service definitions to psql-clj database specs.

Extend next.jdbc's SettableParameter and ReadableColumn protocols so that
PGobject (json/jsonb/enum), SQL arrays, and inet values move between Clojure
data and PostgreSQL without manual wrapping.

The map->parameter / vec->parameter / num->parameter multimethods are the
extension point: companion artifacts, such as psql-clj-gis, add methods for
their SQL types without this namespace depending on them.