Fixed issues for LSTM

Fixes issues related to eclipse/aidge/aidge_core#167.

• Added maxElements input to Stack: @jeromeh I made some change to allow to specify maxElements also through an input. This is actually a necessity to enable static forward dims of a graph with the Stack operator, like in the example above for LSTM;

%%{init: {'flowchart': { 'curve': 'monotoneY'}, 'fontFamily': 'Verdana' } }%%
flowchart TB

LSTM_0("lstm_output<br/><sub><em>(LSTM#0)</em></sub>"):::metaCls_rootCls
Pop_0(<em>Pop#0</em>)
Stack_0(<em>Stack#0</em>)
Identity_0(<em>Identity#0</em>)
Shape_0(<em>Shape#0</em>)
LSTM_0-->|"0&rarr;0"|Stack_0
LSTM_0-->|"0&rarr;0"|output1((out#1)):::outputCls
LSTM_0-->|"1&rarr;0"|output2((out#2)):::outputCls
Pop_0-->|"0&rarr;0"|LSTM_0
Identity_0-->|"0&rarr;0"|Pop_0
Identity_0-->|"0&rarr;0"|Shape_0
Shape_0-->|"0&rarr;1"|Stack_0
input0((in#0)):::inputCls--->|"&rarr;0"|Identity_0
Stack_0--->|"0&rarr;"|output0((out#0)):::outputCls
classDef inputCls fill:#afa
classDef outputCls fill:#ffa
classDef externalCls fill:#ccc
classDef producerCls fill:#ccf
classDef genericCls fill:#f9f9ff,stroke-width:1px,stroke-dasharray: 5 5
classDef metaCls stroke-width:5px
classDef rootCls stroke:#f00
classDef producerCls_rootCls stroke:#f00,fill:#ccf
classDef genericCls_rootCls stroke:#f00,fill:#f9f9ff,stroke-width:1px,stroke-dasharray: 5 5
classDef metaCls_rootCls stroke:#f00,stroke-width:5px

• Make Shape working with forwardDims().

include/aidge/operator/Stack.hpp

@@ -50,7 +50,7 @@ class StackOp
   public:
     static const std::string s_type;
 
-    StackOp(std::uint32_t maxElements);
+    StackOp(std::uint32_t maxElements = 0);
 
     /**
      * @brief Copy-constructor. Copy the operator attributes and its output
@@ -71,6 +71,7 @@ class StackOp
 
     std::set<std::string> getAvailableBackends() const override;
 
+    bool dimsForwarded() const override final;
     bool forwardDims(bool allowDataDependency = false) override final;
     void forward() override;
 
@@ -87,14 +88,14 @@ class StackOp
     }
 
     static const std::vector<std::string> getInputsName() {
-        return {"data_input"};
+        return {"data_input", "max_elements"};
     }
     static const std::vector<std::string> getOutputsName() {
         return {"data_output"};
     }
 };
 
-std::shared_ptr<Node> stack(std::uint32_t maxElements,
+std::shared_ptr<Node> Stack(std::uint32_t maxElements = 0,
                             const std::string &name = "");
 } // namespace Aidge