Add comments and error checks to mem.

mentos/inc/drivers/mem.h

@@ -10,8 +10,14 @@
 
 #pragma once
 
-/// @brief Initializes the memory devices.
-/// @return 0 on success, 1 on error.
+/// @brief Initializes memory devices and registers the null device.
+///
+/// @details This function creates the `/dev/null` device, registers the null
+/// filesystem type, and mounts the null device to the virtual file system. If
+/// any step fails, it logs the error and returns an appropriate error code.
+///
+/// @return 0 on success, -ENODEV if device creation fails, 1 if filesystem
+/// registration or mounting fails.
 int mem_devs_initialize(void);
 
 /// @}