v0.9.4

• Add AST-backed Rustler term encoders with nested, conditional, optional,
  collection, adapter, helper, and fallback field projections.
• Add source-derived Rustler NIF wrappers and Elixir fallback stubs so one
  manifest and the handwritten Rust implementation signatures determine both
  sides of the boundary.
• Discover atom references inside Rust macro token trees and document stable,
  structural Rustler generation workflows.
• Add optional Rustler map decoders and improve option/method result inference.