Add a new Markdown document detailing the AST node structure as it
evolves through the compiler's different stages. This includes a diagram
illustrating the data flow and relationships between the generic
`Node<K, T>` structure and its specialized forms (`UntypedNode`,
`BoundNode`, `TypedNode`, `AnalyzedNode`). The document explains the
`kind` and `ty` payloads for each stage and their significance.
Also removes a deleted file related to a previous optimization plan and
adds new files for future optimization plans.
Michael Schimmel