json stringify with mixed-type variables and type assertions

[cs01]

fix: json stringify with mixed-type variables and type assertions

Summary

• JSON.stringify({ ... } as any) crashed at LLVM opt: the as type assertion wraps the object in a TypeAssertionNode, so arg.type === "type_assertion" instead of "object", bypassing stringifyObjectLiteral and falling through to stringifyNumber. That called generateExpression on the whole object, bitcast the struct pointer to i8*, then passed it as double to sprintf — a type mismatch that opt -O2 rejects.
• Fix: unwrap type_assertion nodes in generateStringify before dispatch, using a named TypeAssertionNode cast (avoids phi node metadata loss from inline as { ... } struct assertions); extract generateStringifyArg() helper.
• Two regression tests added: mixed string+number variable values, and an inline object with a type assertion.

Test plan

• json stringify inline object with mixed string and number variable values passes
• json stringify inline object with type assertion does not crash passes
• All pre-existing JSON stringify tests still pass