Fix 'Pop_Op::forward' that should not be inplace

src/operator/Pop.cpp

@@ -33,7 +33,7 @@ void Aidge::Pop_OpImpl::forward() {
     const Pop_Op& op = dynamic_cast<const Pop_Op&>(mOp);
 
     assert(op.getInput(0) && "missing input #0");
-    *op.getOutput(0) = op.getInput(0)->extract({op.forwardStep()});
+    *op.getOutput(0) = op.getInput(0)->extract({op.forwardStep()}).clone();
 }
 
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