Complete Phase 5B: operator overloading, dunder protocols, decorators

Add dunder method dispatch for user-defined classes, enabling Python-like
operator overloading and special method protocols needed for leanSpec's
BaseUint/Fp classes. Key additions:

- Binary/unary/comparison operator overloading via __add__, __sub__, __mul__,
  __eq__, __lt__, __neg__, etc. with reflected operator fallback (__radd__, etc.)
- Special methods: __str__, __repr__, __len__, __hash__, __bool__, __call__,
  __contains__, __getitem__, __setitem__, __delitem__
- Decorator evaluation: @staticmethod, @classmethod, @Property (with .setter),
  and generic decorators
- New Value types: staticMethod, classMethod, property with descriptor-like
  attribute access semantics
- 25 new passing tests (182 total)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pirapira