Phase 5: Multimethods + Hierarchy system
- types.janet: make-hierarchy, derive*, ancestors, descendants, isa?, underive
- evaluator.janet: defmulti extended with :default and :hierarchy options
+ keyword dispatch-fns wrapped as (fn [x] (get x kw)) for Janet compat
+ hierarchy-based dispatch walks isa? chain when no direct match
- core.janet: real derive, isa?, ancestors, descendants implementations
replacing stubs; core-remove-method, core-remove-all-methods,
core-prefer-method added; new core-bindings entries
- 5 test sections (22-26): hierarchy ops, basic dispatch, :default,
hierarchy dispatch, remove-method — all pass
- 317 tests, 0 failures
a1bfd55b38