Add example and refine local inlining

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.

src/utils/tester.rs

@@ -52,7 +52,10 @@ pub fn run_functional_tests_with_level(level: u32) -> Vec<TestResult> {
                             results.push(TestResult {
                                 name,
                                 success: false,
-                                message: format!("Level {}: Expected {}, got {}", level, expected, val_str),
+                                message: format!(
+                                    "Level {}: Expected {}, got {}",
+                                    level, expected, val_str
+                                ),
                             });
                         }
                     }