Resolve "Bad MetaOp attributes"

Context

Closes #208 (closed)

Now the interface is:

>>> import aidge_core as ai
>>> import aidge_onnx
>>> import aidge_backend_cpu
>>>
>>> op = ai.PaddedConv2DOp([3,3], padding_dims=[1,1,1,1])
>>>
>>> op.attr
AttrDict({'Conv2D_0': AttrDict({'stride_dims': [1, 1], 'dilation_dims': [1, 1], 'kernel_dims': [3, 3]}), 'Pad2D_0': AttrDict({'begin_end_borders': [1, 1, 1, 1], 'border_type': <pad_border_type.Constant: 0>, 'border_value': 0.0})})
>>>
>>> op.attr.Conv2D_0
AttrDict({'stride_dims': [1, 1], 'dilation_dims': [1, 1], 'kernel_dims': [3, 3]})
>>>
>>> val = op.attr.Conv2D_0.dilation_dims
>>> val
[1, 1]

Since the attribute list is created at the construction of the MetaOperator, it cannot be updated with new nodes, but its values are still updated automatically.

The access time is much lower since the list is not created each time an element needs to be accessed.

Modified files

Detailed major modifications