- Add read support for system-level input registers:
- FIRMWARE_VERSION_MAJOR_MINOR (0xF0)
- FIRMWARE_VERSION_PATCH (0xF1)
- DEVICE_STATUS (0xF2)
- Use enums for register addresses to improve readability.
- Implement a workaround for a Kconfig issue by hardcoding the firmware version.
- Stabilize multi-register reads by returning 0 for unhandled input registers instead of an exception.
- NOTE: Writing to holding registers is currently unstable with mbpoll and will be addressed separately.