Fixed wrong pid bug

The issue was that the thread ID wasn't factored in. A presumption was,
that FUSE already returned the PID, not TID. The issue was fixed by
implementing a function that translates the TID to PID.

src/proc_operations.h

@@ -22,4 +22,13 @@ char *get_process_name_by_pid(const int pid);
  */
 pid_t get_parent_pid(pid_t pid);
 
+/**
+ * @brief Returns the PID of the main thread (i.e., the process ID) of the
+ * process that the given thread ID (tid) belongs to.
+ *
+ * @param tid The thread ID (TID) of any thread in the process.
+ * @return pid_t The process ID (main thread's PID), or -1 on error.
+ */
+pid_t get_main_thread_pid(pid_t tid);
+
 #endif // !PROC_OPERATIONS