feat(lib): Introduce adc_sensor library

Adds a new `adc_sensor` library to abstract reading analog values from ADC channels. The output of this library is currently simulated.

This library is now used by the `modbus_server` to read the motor current and the main supply voltage, replacing the previous implementation. This change improves modularity by centralizing ADC-related code into a dedicated module.

The build system has been updated to include the new library.

software/lib/adc_sensor/Kconfig

@@ -0,0 +1,16 @@
+config ADC_SENSOR
+	bool "ADC sensor library"
+	default y
+	help
+	  Enable ADC sensor library for voltage and current measurements.
+
+if ADC_SENSOR
+
+config ADC_SENSOR_SIMULATED
+	bool "Use simulated ADC readings"
+	default y
+	help
+	  Use simulated values instead of real ADC readings.
+	  Voltage: 12000mV, Current: 45mA
+
+endif # ADC_SENSOR