Add <atomic> include and fix OpenMP shared directive

Include the <atomic> header where needed to ensure proper functionality. Update OpenMP parallel region directives to explicitly declare the shared variable `counter` to avoid potential issues.

Author: allnes

tasks/example/all/src/ops_all.cpp

@@ -2,6 +2,7 @@
 
 #include <mpi.h>
 
+#include <atomic>
 #include <cmath>
 #include <cstddef>
 #include <functional>
@@ -44,7 +45,7 @@ bool NesterovATestTaskALL::RunImpl() {
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   if (rank == 0) {
     std::atomic<int> counter(0);
-#pragma omp parallel default(none)
+#pragma omp parallel default(none) shared(counter)
     {
       counter++;
     }

tasks/example/omp/src/ops_omp.cpp

@@ -1,5 +1,6 @@
 #include "example/omp/include/ops_omp.hpp"
 
+#include <atomic>
 #include <cmath>
 #include <cstddef>
 #include <vector>
@@ -34,7 +35,7 @@ bool NesterovATestTaskOMP::RunImpl() {
   GetOutput() *= num_threads;
 
   std::atomic<int> counter(0);
-#pragma omp parallel default(none)
+#pragma omp parallel default(none) shared(counter)
   {
     counter++;
   }

tasks/example/stl/src/ops_stl.cpp

@@ -1,5 +1,6 @@
 #include "example/stl/include/ops_stl.hpp"
 
+#include <atomic>
 #include <cmath>
 #include <cstddef>
 #include <functional>

tasks/example/tbb/src/ops_tbb.cpp

@@ -2,6 +2,7 @@
 
 #include <tbb/tbb.h>
 
+#include <atomic>
 #include <cmath>
 #include <core/util/include/util.hpp>
 #include <cstddef>