Add a new example file `examples/def_local_inlining.myc` to demonstrate
and test local inlining.
Refine the optimizer to handle local inlining more robustly by:
- Passing a `SubstitutionMap` to `visit_node` to track local variable
substitutions.
- Enabling constant propagation for local variables by checking
`sub.locals` in `BoundKind::Get`.
- Updating `BoundKind::DefLocal` and `BoundKind::Set` to maintain the
substitution map for local variables.
- Adjusting `try_beta_reduce` to use the optimizer's `visit_node` with
the substitution map for inlining.
- Re-indexing upvalues correctly when inlining captured variables into
lambdas.
Michael Schimmel
b2e010e755