Restore Delegator.delegating_block

[hsbt]

#53 (comment)

[Copilot]

Pull request overview

This PR restores the Delegator.delegating_block method, replacing the previous delegating_code approach for defining special (non-standard) method names in delegated classes. The change simplifies the implementation by using a lambda with define_method instead of string-based code generation with module_eval.

• Replaces delegating_code (which generated evaluable source code strings) with delegating_block (which returns a lambda)
• Simplifies method definition for special methods (operators like [], ==, etc.) by using define_method with a lambda instead of module_eval with generated source code
• Maintains proper keyword argument handling through .ruby2_keywords annotation on the lambda

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