Refactor build_where_text to use psycopg2.sql

[hollowtree11]

The current implementation of build_where_text in PostgresConnector relies on manual string concatenation and f-strings to build SQL queries. Manual SQL building is prone to security vulnerabilities and is often where third-party library updates break code. We should refactor this method to use the psycopg2.sql module. This allows us to build queries using SQL, Identifier, and Placeholder objects, ensuring that table names, column names, and values are handled safely by the driver.