docs: Add Doxygen comments to library files

Added Doxygen-style comments to all C source and header files in the
 and  directories. This improves
code documentation and enables VSCode tooltip help.

Additionally, short inline comments were added to all global variables
for better clarity.

software/lib/adc_sensor/adc_sensor.c

@@ -1,3 +1,12 @@
+/**
+ * @file adc_sensor.c
+ * @brief Implementation of the ADC sensor library.
+ *
+ * This file contains the implementation for initializing and reading from ADC sensors.
+ * It currently provides simulated values for voltage and current, with placeholders
+ * for real hardware ADC implementation.
+ */
+
 #include <zephyr/kernel.h>
 #include <zephyr/logging/log.h>
 #include <lib/adc_sensor.h>
@@ -8,7 +17,7 @@ LOG_MODULE_REGISTER(adc_sensor, LOG_LEVEL_INF);
 #define SIMULATED_VOLTAGE_MV 12000
 #define SIMULATED_CURRENT_MA 45
 
-static bool initialized = false;
+static bool initialized = false; // Flag to indicate if the ADC sensor is initialized
 
 int adc_sensor_init(void)
 {