Breaking: collect_assigned_vars function removed from if_phi.rs
Changes:
- Delete collect_assigned_vars() function (35 lines)
- Make JoinIR route the default in loop_builder.rs
- Rewrite collect_assigned_vars_via_joinir() with ast_to_json support
- Now detects both Local declarations and Assignment nodes
- Add extract_vars_from_json_stmts/stmt helpers
- Update tests to use new implementation
- phase40_joinir_detects_local_declarations
- phase40_joinir_nested_if_local
Test results: 407 passed, 11 failed (same as before, no regression)
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Co-Authored-By: Claude <noreply@anthropic.com>
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