AQFP optimization methods

[aletempiac]

This PR contains the algorithms presented at ASP-DAC 2023 to optimize buffers and splitters in AQFP circuits.

Additions:

• Three new ways of inserting buffers and splitters such that the resulting depth of the AQFP circuit is optimal (ALAP_depth, ASAP_depth, better_depth) in buffer_insertion.hpp
• Utilities to clean and rebuild AQFP networks
• Minimum-area register retiming
• AQFP buffer and splitter optimization using minimum-area retiming
• A new network type generic.hpp with no strashing. In this network all the nodes are represented in the graph including POs. Moreover, this network includes new types such as box input terminal, box output terminal, and register. This network type is used for retiming
• Choice view to save equivalent classes in networks
• Experiment to reproduce the results in the paper "Depth-optimal Buffer and Splitter Insertion and Optimization in AQFP Circuits", ASP-DAC 2023, by Alessandro Tempia Calvino and Giovanni De Micheli.

Modifications for compatibility

• buffered.hpp: adding an AQFP buffered network
• storage.hpp: adding a definition of storage that doesn't support strashing
• fanout_view.hpp: fanout view computes the fanout for all the internal nodes (all the nodes excluding constants and PIs, buffers included) in buffered networks. For other types of networks, it computes the fanout for all the gates
• topo_view: includes a deterministic shuffling of the topological order

[lee30sonia]

FYI: I am working on a renovation of AQFP assumptions, buffer counting and insertion, which will likely lead to conflicts in the file buffer_insertion.hpp. Thus I copied the current version of this file in this PR to my working branch and start from there. If you will make any further modifications to this file before merging this PR, please let me know.