fix: use pgfree for libpq mallocs

[ColinKYuen]

Summary

Uses libqpq's Free for libqpq malloc'd String

Description

Changes the generic free() function for the error message string allocated by PQconninfoParse(..) to use libpq's PQfreemem(..)

As per PostgreSQL's libqpq documents, when using PQconninfoParse(..):

... After processing the options array, free it by passing it to PQconninfoFree. If this is not done, some memory is leaked for each call to PQconninfoParse. Conversely, if an error occurs and errmsg is not NULL, be sure to free the error string using PQfreemem.

Additional information on PQfreemem, this change is only needed for Windows

Frees memory allocated by libpq, particularly PQescapeByteaConn, PQescapeBytea, PQunescapeBytea, and PQnotifies. It is particularly important that this function, rather than free(), be used on Microsoft Windows. This is because allocating memory in a DLL and releasing it in the application works only if multithreaded/single-threaded, release/debug, and static/dynamic flags are the same for the DLL and the application. On non-Microsoft Windows platforms, this function is the same as the standard library function free().