The egg/z3 Optimizer

teeny-compiler depends on egg (e-graph based equality saturation) for graph-level optimization/rewriting as part of the FXGraph compilation pipeline (see Compilation Flow). teeny-fxgraph and teeny-torch also depend on egg.

z3 (SMT solving) is referenced in project documentation as a planned complement to egg for optimization, but is not currently wired up as a dependency of any workspace crate — treat it as roadmap, not shipped functionality, until a z3 dependency actually appears in a Cargo.toml.

TODO: document the specific e-graph rewrite rules and what they optimize for, once this layer has enough surface area to be worth a dedicated walkthrough.