Simplify single-test to match vendor capture exactly

Remove send_test_config() call - vendor software doesn't send 8C 2B for
each single test, only when changing modes. Remove set_integration_time()
from spectrometer.py - vendor doesn't send 8C 01 either.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

spectrometer.py

@@ -16,7 +16,6 @@ def measure():
     dev = HPCS6500(port)
     try:
         dev.identify()
-        dev.set_integration_time(0)  # auto
         reading = dev.take_single_reading()
     finally:
         dev.close()