Add bindings for PQ tracing functions

Add bindings for PQ tracing functions

Since we cannot pass a file descriptor as a FILE value, as expected by
PQtrace(), PGconn.trace() method accepts a 'fileno: int' value. This is
then used to build an stdio's FILE value through fdopen(). The latter
also needs a binding in ctypes. This only works on Linux platform.

In _pq_ctypes.pyi, fdopen() and PQtrace() are not autogenerated because
of the needed '# type: ignore' (similar to existing ones).

PQsetTraceFlags() is new from libpq 14, so we declare it conditionally.