fix save_static_scheduling_diagram when using sequential tiling

What commit version of aidge do you use

• aidge_core: 4d5711e4
• aidge_export_cpp: 9f86629bbc179698a89b4a85d2bc79a567a04522

Problem description

Related implem #280 (closed) made it possible to choose a "compute speed"/memory compromise as shown on the two examples below. (It is an encoder made of 1DCNNs, that is tiled in multiple slice for sequential computing, reducing the memory peak)

However, the save_static_scheduling_diagram() and save_scheduling_diagram() are still not aware of this and show a wrong scheduling as seen below.

With 2 slices, ram_peam= 683kB, time=25ms:

With 20 slices ram_peak=200kB, Time=250(ms?):

(issue for the mermaid scheduling diagram here @pierregaillard @olivierbichler )