Flowgraph constructions

[bdngo]

This PR implements a functioning prototype for flowgraphs, a more idiomatic way of representing VLSI flows. With this, instead of stringing multiple CLI calls to hammer-vlsi, one can construct a Graph consisting of Nodes encoding Hammer actions. The feature makes heavy use of the networking package NetworkX to manipulate flowgraphs. Flowgraphs are nothing more than Python dataclass instantiations, making them modular and reusable. Ideally, flowgraphs and the current workflow for Hammer will coexist for now, with pending ports of advanced Hammer features.

Related PRs / Issues

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• Change to core Hammer
• Change to a Hammer plugin
• Other

Contributor Checklist:

• Did you set master as the base branch?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you update the poetry.lock file if you updated the requirements in pyproject.toml?
• (If applicable) Did you add a unit test demonstrating the PR?
• (If applicable) Did you run this through the e2e integration tests?
• (If applicable) Did you update the submodules in e2e/ if this feature depends on updated plugins?

[harrisonliew]

I'm going to wait til after the current tapeout to merge this. So, if you have the time, I'd like to see the e2e Makefile duplicated in the form of a flowgraph. Else, it can come as a future PR.