rfe9757 - python events test queries could use dedicated backends
rfe9757 - python events test queries could use dedicated backends

Changed Phase 4, query phase, to use dedicated backends (sessions)
to increase queries per second potential.

During testing since it is faster, I got a divide-by-zero error
when using a time difference in the denominator. All such places
are now protected.

No API changes, so no release notes.

Tests added for:     None
make test-suite run? No - but events test was run

franzinc/agraph-python,franzinc/agraph-python,franzinc/agraph-python,franzinc/agraph-python