Re-enable PostgreSQL tests that pass on 16 and 18

[velo]

Re-test of every @ExcludeIn containing POSTGRESQL (17 entries) on the current postgis/postgis:16-3.4-alpine and on postgis/postgis:18-3.6-alpine. Both give identical results, so no image bump.

Re-enabled (2): dates, subQuery_params. Both pass in PostgreSQLSuiteTest and PostgreSQLLiteralsSuiteTest.

Still excluded:

Tests	Reason
BeanPopulationBase (3)	EMPLOYEE.ID is NOT NULL without default in the PostgreSQL schema
random2	no rand(n) in PostgreSQL
number_as_boolean	integer bound to a boolean column
string_indexOf	INDEX_OF_2ARGS template ignores the start position (// FIXME in PostgreSQLTemplates)
merge_with_keys_Null_Id	merge returns a null generated key
dump_types	PgDatabaseMetaData.getAttributes not implemented

Found along the way, not fixed here:

• The r2dbc PostgreSQL suites never run: both are public abstract class. When made concrete, setup crashes (initPostgreSQL calls pstmt.add() once too often) and Connections.getPostgreSQL() uses port 5433 while compose and CI expose 5432.
• PostgreSQL 18 would need 22 new keywords in keywords/postgresql (JSON_TABLE, MERGE_ACTION, ...).