Use nanosecond-based requestid to avoid collisions in convert operations

The previous implementation used int(time.time()) which returns seconds,
causing requestid collisions when multiple convert operations are created
within the same second. This caused flaky test failures with error:
"could not insert object, uniqueness constraint was violated"

Change to time.time_ns() % (2**32) which provides nanosecond resolution
while staying within uint32_t bounds, effectively eliminating collisions.