* Prototype document network level into node insertion
* Implement Convert trait / node for places we can't use Into
* Add isize/usize and i128/u128 implementations for Convert trait
* Factor out substitutions into preprocessor crate
* Simplify layer node further
* Code review
* Mark preprocessed networks as generated
* Revert changes to layer node definition
* Skip generated flag for serialization
* Don't expand for tests
* Code review
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Co-authored-by: Keavon Chambers <keavon@keavon.com>