Improve type conversion of SPI_processed in Python

Improve type conversion of SPI_processed in Python

The previous code converted SPI_processed to a Python float if it didn't
fit into a Python int.  But Python longs have unlimited precision, so
use that instead in all cases.

As in eee50a8d4c389171ad5180568a7221f7e9b28f09, we use the Python
LongLong API unconditionally for simplicity.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>