MergedEdge class for merging node functionality

[Stevengre]

Here is the alternative implementation for this PR.

• commit 1: introduce the new class MergedEdge
• commit 2: add to_rule function to MergedEdge for CSE
• commit 3: add corresponding functions like Edge for MergedEdge
• commit 4: modify Edge.to_rule related functions for CSE
• commit 5: modify KCFGShow for MergedEdge
• commit 6: modify KCFGViewer for MergedEdge

[Stevengre]

Compared to #4600, the impact of this implementation is smaller, but it still has some effects. Specifically, for KCFG.minimize, the lift_edge_edge and lift_split_edge functions won’t work with the MergedEdge, which will prevent obtaining a summary for a function that uses a summary. However, this approach still seems simpler than #4600. I’ll start a separate PR to refactor the existing KCFG.minimize.

[tothtamas28]

Please add some unit tests for a KCFG containing MergedEdge instances.

[Stevengre]

Please add some unit tests for a KCFG containing MergedEdge instances.

This commit adds these unit tests, but leaves the unit test for minimization for another PR.

[tothtamas28]

LGTM. Please test on evm-semantics before merging.

[Stevengre]

• make cov-unit passed for evm-semantics
• make cov-unit passed for kontrol

[tothtamas28]

• make cov-unit passed for evm-semantics
• make cov-unit passed for kontrol

Please also run integration tests for evm-semantics.

[Stevengre]

After spending a long time configuring, I still couldn’t get the evm-semantics integration tests to run. So I decided to submit it as a PR and use the existing CI for testing.

[Stevengre]

This PR encountered the same error as the previous PR, and it also failed the Nix tests.

Therefore, I believe the introduction of the merged edge doesn’t affect evm-semantics. It might be some other updates in the pyk repository that are impacting evm-semantics, but I’m not entirely sure.