Add Corsair Commander DUO support

Add a new Corsair Commander DUO driver with fan status/control, ARGB lighting,
and capture-backed Device Memory lighting support.

The driver supports the DUO's two PWM fan channels and two standard 5 V ARGB
ports. Software lighting supports off and fixed, while Device Memory
lighting supports off, fixed, and rainbow through --non-volatile.
Device Memory lighting is intentionally limited to the observed global hardware
lighting endpoint (65 6d): fixed/off use the captured 7e 20 payload format,
and rainbow uses the captured 02 a4 payload. The implementation deliberately
does not write the nearby 61/62/63 6d endpoints because the captures and
Commander Core protocol parallels indicate those are cooling/profile data.

The user guide and protocol notes document the remaining limitations: DUO
hardware lighting is global rather than per-port, iCUE LINK devices are not
supported by this driver, and advanced Device Memory effects such as speed,
direction, palettes, readback APIs, and broader hardware profile management are
out of scope for this change.

Hardware verification was performed on a Commander DUO. Persistent rainbow and
persistent fixed 3200ff (50R 0G 255B) were written with --non-volatile and
visually confirmed to persist.

Related: Commander DUO USB captures used for protocol reverse engineering.

Checklist:

• Adhere to the development process
• Conform to the style guide
• Verify that the changes work as expected on real hardware
• Add automated tests cases
• Verify that all (other) automated tests (still) pass
• Update/add documentation
  • README, with "new/changed in" notes
  • applicable docs/*guide.md device guides, with "new/changed in" notes
  • liquidctl.8 Linux/Unix/Mac OS man page
  • protocol documentation in docs/developer/protocol
• Submit relevant data, scripts or dissectors to https://github.com/liquidctl/collected-device-data

New CLI flag?

• Adjust the completion scripts in extra/completions/

New device?

• Regenerate extra/linux/71-liquidctl.rules (instructions in the file header)
• Add entry to the README's supported device list with applicable notes and git MRLV

New driver?

• Document the protocol in docs/developer/protocol/

Verification performed:

• lsp_diagnostics clean for liquidctl/driver/__init__.py,
  liquidctl/driver/commander_duo.py, and tests/test_commander_duo.py
• .venv/bin/python -m py_compile liquidctl/driver/__init__.py
liquidctl/driver/commander_duo.py tests/test_commander_duo.py
• .venv/bin/python -m pytest tests/test_commander_duo.py (22 passed)
• driver import smoke test for commander_duo registration
• git diff --check for tracked PR files