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/include/lib/adc_sensor.h

@@ -0,0 +1,27 @@
+#ifndef ADC_SENSOR_H
+#define ADC_SENSOR_H
+
+#include <stdint.h>
+
+/**
+ * @brief Initialize the ADC sensor system
+ * 
+ * @return 0 on success, negative error code on failure
+ */
+int adc_sensor_init(void);
+
+/**
+ * @brief Get supply voltage reading in millivolts
+ * 
+ * @return Voltage in millivolts (currently simulated: 12000mV)
+ */
+uint16_t adc_sensor_get_voltage_mv(void);
+
+/**
+ * @brief Get motor current reading in milliamps
+ * 
+ * @return Current in milliamps (currently simulated: 45mA)
+ */
+uint16_t adc_sensor_get_current_ma(void);
+
+#endif /* ADC_SENSOR_H */