fix: use emitCallVoid for describe/test callbacks

[cs01]

Summary

• describe() and test() callbacks were called with emitCall("double", ...) but the lambda functions return void
• this generated invalid LLVM IR (calling a void function and expecting a double return)
• switched to emitCallVoid and added closure environment pointer passing for callbacks with captures

the native compiler still crashes on nested describe+test (separate self-hosting bug with nested function calls inside lambda bodies), so describe.ts remains @test-skip. but the generated IR is now correct.

Test plan

• npm run verify:quick passes
• JS compiler correctly builds and runs describe.ts