fix(codegen): harden validation edge cases

[luisleo526]

Summary

• support typed drawing array constructors and drawing-handle na defaults
• improve function parameter/return/type inference for validation strategies
• add function-scoped var one-shot initialization
• reject mixed-callsite UDF request.security timeframe params instead of silently miscompiling

Verification

• python3 -m pytest tests/ -q
• pinescript-scrapper targeted validations
• broad pinescript-scrapper baseline: 100 exported strategies, ok=86, no-trades=3, transpile-error=11, compile-error=0
• engine corpus after paired engine test PR: 252 strategies, excellent=251, anomaly=1, fail=0