Matmul rework

The behavior of the reworked MatMul on the arguments in the following way.
- If both arguments are 2-D they are multiplied like conventional matrices.
- If either argument is N-D, N > 2, it is treated as a stack of matrices residing in the last two indexes.
Exp: For the MatMul of tensor A of shape (3,3,2) with tensor B of shape (3,2,4), A is a stack of three 2D matrices each of shape (3,2), and B is a stack of 3 2D matrices, each of shape (2,4).

unit_tests/data/Test_TensorImpl.cpp

@@ -19,7 +19,7 @@
 
 using namespace Aidge;
 
-TEST_CASE("Tensor creation") {
+TEST_CASE("[backend_cpu/data] Tensor(constructor)","[Tensor]") {
   SECTION("from const array") {
     Tensor x = Array3D<int, 2, 2, 2>{{{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}}};
 
@@ -59,7 +59,7 @@ TEST_CASE("Tensor creation") {
   }
 }
 
-TEST_CASE("Tensor methods") {
+TEST_CASE("[backend_cpu/data] Tensor(methods)", "[Tensor]") {
   Tensor x = Array3D<int, 2, 2, 2>{{
     {{1, 2},
      {3, 4}},
@@ -89,7 +89,7 @@ TEST_CASE("Tensor methods") {
     REQUIRE(y.getImpl() == x.getImpl());
     REQUIRE(approxEq<int>(y, Array1D<int, 2>{{3, 4}}));
     REQUIRE(y.isContiguous());
-    
+
     Tensor y2 = x.extract({0, 1, 1}, {2, 1, 1});
     REQUIRE(y2.getImpl() == x.getImpl());
     REQUIRE(!y2.isContiguous());