common: Make use of [[nodiscard]] where applicable

Now that clang-format makes [[nodiscard]] attributes format sensibly, we
can apply them to several functions within the common library to allow
the compiler to complain about any misuses of the functions.

src/common/memory_detect.h

@@ -17,6 +17,6 @@ struct MemoryInfo {
  * Gets the memory info of the host system
  * @return Reference to a MemoryInfo struct with the physical and swap memory sizes in bytes
  */
-const MemoryInfo& GetMemInfo();
+[[nodiscard]] const MemoryInfo& GetMemInfo();
 
 } // namespace Common