chore: make is_memory64 check robust

[venkkatesh-sekar]

1. If the module's memory (index 0) is 32-bit, it returns false.
2. If the memory is 64-bit:
   • If ic0.msg_reply_data_append is NOT imported, it assumes 64-bit usage and returns true.
   • If ic0.msg_reply_data_append IS imported, it checks the function signature.
   • If the parameters are i64, it returns true.
   • Otherwise (e.g., i32), it returns false.