Implement a custom graph renaming routine for inline

[jbachurski]

Addresses #82 by avoiding adding extraneous Identity nodes when inlining and supporting subgraph renaming

• Reimplements the onnx.compose.add_prefix_graph to make it more flexible.
• Slightly expands Spox scopes to support 'anonymous' reserved names, which don't have an associated Var/Node, but are nevertheless marked as taken. This is because not all inlined nodes/values have a respective Var/Node.

[cbourjau]

Great! Thanks! I just have some minor suggestions/questions.

This is because not all inlined nodes/values have a respective Var/Node.

Could you expand on this a bit? Do you mean the nodes inside a subgraph?

[jbachurski]

Looks like due to the conda ONNX version bump, the CI is now failing on opset generation, so #83 will fix this :)

[jbachurski]

I also added an explicit proto-based test, and one for subgraph lists as there is no practical example that can be constructed there (no node uses a list of subgraphs...). This is since we are now straying from the ONNX utility which would have some tests itself. Maybe I'll upstream the new one at some point?

This is because not all inlined nodes/values have a respective Var/Node.

Could you expand on this a bit? Do you mean the nodes inside a subgraph?

@cbourjau Yeah - say an inlined ModelProto has an input X and output Y, and an intermediate Z. Then there is a Var corresponding to X and another for Y, but there will be no explicit variable for Z in the Spox graph. However, it does have to reserve some name for itself in-scope to avoid e.g. other inlines of the same model using that name. So the ScopeSpace object marks whatever name was used for Z as taken with the newly applied patch.

[cbourjau]

Thanks for the clarification :)