Source Code Generator for Snap.Hutao

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1. Every IncrementalValue(s)Provider<T>'s step result should be an IEquatable<T> to make it really becomes incremental.
2. So the intermediate models should be a record (class/struct) if possible
3. Intermediate array/enumerable should be a ImmutableArray<T> if possible, the pipeline use IA internally and has special check for it.