The memory manager should allow to ignore nodes

Context

The memory manager generates memory offsets used by the export to store the parameters and feature maps.

Issue

Sometimes, some producers are not needed in the context of the export. For instance, the scaling factor (which is a Producer in Aidge) may be stored as a macro when exported (instead of a table like other parameters).
The memory manager does not need to save memory space for these kind of nodes, so we may need a way to indicate that a node is optionnal for the export.