Matmul rework

[ADD] support for Multi-dimensional Matrix Multiplication, following numpy MatMul operation specificities.

In the context of Multi-dimensional MatMul, we consider an N-Dim Tensor as a stack of 2-D matrices having as shape the last two dimensions of the Tensor.

From Numpy documentation:

The behavior depends 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 and broadcast accordingly.
• If the first argument is 1-D, it is promoted to a matrix by prepending a 1 to its dimensions. After matrix multiplication the prepended 1 is removed.
• If the second argument is 1-D, it is promoted to a matrix by appending a 1 to its dimensions. After matrix multiplication the appended 1 is removed.

include/aidge/operator/MatMul.hpp

@@ -55,23 +55,7 @@ public:
     }
 
 
-    void computeOutputDims() override final {
-        if (!getInput(0)->empty() && !getInput(1)->empty())
-        {
-            std::vector<std::size_t> outDims;
-            for (std::size_t i = 0; i < getInput(0)->nbDims()-1; i++)
-            {
-                outDims.push_back(getInput(0)->dims()[i]);
-            }
-            size_t secondToLastIdx = getInput(1)->nbDims() > 1 ? getInput(1)->nbDims() - 2 : 0;
-            for (std::size_t i = 0; i < getInput(1)->nbDims(); i++)
-            {
-                if(i != secondToLastIdx)
-                   outDims.push_back(getInput(1)->dims()[i]);
-            }     
-            mOutputs[0]->resize(outDims);
-        }
-    }
+    void computeOutputDims() override final;
 
 
     void setBackend(const std::string& name, DeviceIdx_t device = 0) override {