[Fix] Producer clone and Tensor copy

Context

Closes #207 (closed)

Major modifications

• Tensor

  • add compound assignment operator (+=, -=, *=, /=) with Tensor and arithmetic values
  • add operator(+, -, *, /) with arithmetic values
  • add friend symetric operator (+, -, *) with arithmetic values
  • add fmt parsing function (now you can display a Tensor with fmt)
  • Add move assignment operator
  • Fix 'Tensor::clone()' if original Tensor has no implementation
  • Change Tensor::operator= behaviour to always perform a shallow copy in case of copy constructor/assignment operator calls

• Pop_Op: fix kernel that should not be inplace

• Data: add copy/move constructor/assignment operator

src/operator/Producer.cpp

@@ -44,7 +44,7 @@ Aidge::Producer_Op::Producer_Op(const std::shared_ptr<Aidge::Tensor> tensor, boo
         attr<ProdAttr::Constant>(constant)))
 {
     mOutputs[0] = tensor; // copy the pointer of the Tensor
-    if (mOutputs[0]->getImpl() && Registrar<Producer_Op>::exists({mOutputs[0]->getImpl()->backend()})){
+    if (mOutputs[0] && mOutputs[0]->hasImpl() && Registrar<Producer_Op>::exists({mOutputs[0]->getImpl()->backend()})){
         SET_IMPL_MACRO(Producer_Op, *this, mOutputs[0]->getImpl()->backend());
     }
     else {
@@ -61,7 +61,7 @@ Aidge::Producer_Op::Producer_Op(const Aidge::Producer_Op& op)
     : OperatorTensor(op),
       mAttributes(op.mAttributes)
 {
-    mOutputs[0] = std::make_shared<Tensor>(*(op.getOutput(0)));
+    *mOutputs[0] = *(op.getOutput(0));
     if (mOutputs[0]->getImpl() && Registrar<Producer_Op>::exists({mOutputs[0]->getImpl()->backend()})){
         SET_IMPL_MACRO(Producer_Op, *this, mOutputs[0]->getImpl()->backend());
     }
@@ -71,7 +71,12 @@ Aidge::Producer_Op::Producer_Op(const Aidge::Producer_Op& op)
 }
 
 std::shared_ptr<Aidge::Operator> Aidge::Producer_Op::clone() const {
-    return std::make_shared<Producer_Op>(*this);
+    // mOutput cannot be nullptr because of OperatorTensor constructor
+    std::shared_ptr<Tensor> newTensor = std::make_shared<Tensor>(mOutputs[0]->clone());
+
+    std::shared_ptr<Producer_Op> newOp = std::make_shared<Producer_Op>(newTensor, constant());
+
+    return newOp;
 }
 
 void Aidge::Producer_Op::setBackend(const std::string& name, Aidge::DeviceIdx_t device) {