Added comprehensive test function with 9 sub-tests that directly match the code examples from issue #961: - int8 overflow wrapping - uint32 to float64 to int32 conversion - untyped constant with typed variable - int8 arithmetic edge cases - int8 multiplication overflow - signed to unsigned conversion - unsigned to signed conversion - sign extension - truncation All tests pass with both standard Go and llgo compiler, ensuring consistent behavior between the two implementations. Related to #961 Generated with [codeagent](https://github.com/qbox/codeagent) Co-authored-by: cpunion <cpunion@users.noreply.github.com>