[Refactor] Rename "DAG" to "CircuitSeq"

[xumingkuan]

The name DAG is a bit confusing in that the term "DAG" is not the best name to describe it. It is actually the "Sequence Representation" in our paper (https://arxiv.org/pdf/2204.09033.pdf, page 4, section 3.1).

I am considering renaming it to CircuitSeq to avoid confusion. Here is the complete renaming plan:

• DAG -> CircuitSeq
• DAGNode -> CircuitWire
• DAGHyperEdge -> CircuitGate (I am not sure if this is clear enough that this is a gate in a circuit and easily distinguishable with the abstract Gate type)
• DAG::nodes -> CircuitSeq::wires
• DAG::edges -> CircuitSeq::gates
• DAGNode::input_edges -> CircuitWire::input_gates
• DAGNode::output_edges -> CircuitWire::output_gates
• DAGHyperEdge::input_nodes -> CircuitGate::input_wires
• DAGHyperEdge::output_nodes -> CircuitGate::output_wires
• Graph::to_dag -> Graph::to_circuit_sequence

Do you think the new names are clear? Any suggestions are welcome.

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Edit after merging #61: the class name is renamed, but there are a lot of variable names still being dag. Help wanted for renaming these to seq :)

[xumingkuan]

If there are no suggestions, I will start refactoring.

[jiazhihao]

These renames look good to me. We should also rename TASOGraph to Graph, since our current graph implementation is quite different from the original TASOGraph. @zikun-li @Co1lin What do you think?

[xumingkuan]

These renames look good to me. We should also rename TASOGraph to Graph, since our current graph implementation is quite different from the original TASOGraph. @zikun-li @Co1lin What do you think?

I think this is already renamed. But the file name is still tasograph/tasograph.h -- shall we also rename that to graph/graph.h?