Change 1D attribute Tensors for scalar Tensors and use compound assignment...

Context

See aidge_core!273 (merged) related to aidge_core#207 (closed)

Change 1D attribute Tensors for scalar Tensors and use compound assignment operators on 'Parameter' to avoid reset of 'mGrad' attribute.

unit_tests/optimizer/Test_Adam.cpp

@@ -146,7 +146,7 @@ TEST_CASE("[learning/Adam] update", "[Optimizer][Adam]") {
                 for (std::size_t t = 0; t < nb_tensors; ++t) {
                     const Tensor tmpt1= *(opt.parameters().at(t));
                     const Tensor tmpt2= *tensors[t];
-                    REQUIRE(approxEq<float,float>(tmpt2, tmpt1, 1e-5f, 1e-8f));
+                    REQUIRE(approxEq<float,float>(tmpt2, tmpt1, 1e-5f, 1e-7f));
                 }
             }
         }