Add a RAWSEL sweep example that captures one RAW file per channel

[mikelangmayr]

• Adds python/examples/raw_channel_sweep.py, which loops RAWSEL through the Python bindings taking one exposure per channel, since the Archon captures raw for a single channel at a time
• Sets RAWSEL before each exposure, because the controller acquires raw samples while it fills the buffer
• Reports the module inventory from SYSTEM rather than deriving a slot from RAWSEL, whose stride the manual and the Archon GUI disagree on
• Optional overrides for the RAW geometry keys, and it leaves RAWENABLE off on the way out
• Verified against the emulator: three channels swept, each producing a RAW file whose header carries its own RAWSEL alongside the paired image
• Clean under ruff, 10.00/10 under pylint