[Core] Implement executable incant call model with recursion support

[jbatte47]

Problem

incant declarations are currently treated more like metadata/patterns than fully executable function values with call frames and lexical environments.

To support real computation (including recursion), incant execution semantics must be formalized.

Scope

• Implement executable incant call model with:
  • argument binding
  • lexical scope handling
  • return/yield propagation
• Support guarded recursive calls.
• Preserve behavior for current non-recursive examples.

Deliverables

• Runtime call-frame/environment mechanism for incant calls.
• Tests for direct call, nested call, and recursion with base case.
• Developer notes describing recursion safety expectations.

Acceptance Criteria

• Recursive sample program executes correctly with deterministic result.
• Existing examples continue to run.
• Runtime remains stable under bounded recursion depth.

Validation Checklist

• Add recursion fixtures (e.g., factorial-like with base case).
• Add tests for parameter scoping and return behavior.
• Run full examples suite.

Non-goals

• Tail-call optimization.
• Full closure/lambda language surface.
• Advanced optimizer work.