Introduces separate Modbus holding registers for configurable end-position
current thresholds for both opening and closing valve movements.
- Added REG_HOLDING_VALVE_END_CURRENT_THRESHOLD_OPEN_MA and
REG_HOLDING_VALVE_END_CURRENT_THRESHOLD_CLOSE_MA to modbus_server.h.
- Modified valve.c to use these new thresholds and save/load them via settings.
- Added new setter functions to valve.h.
- Created new shell_valve library with commands to set/get these thresholds.
- Updated modbus_tool.py to include new menu options for setting thresholds.
- Updated docs/modbus-registers.de.md to document the new registers.
This enhances the flexibility and calibration of the valve control system.