I don't think what you want us even possible. How would such guarantees even look like? "Hello, we are a serious cybersec firm and we have evaluated the code and it's pretty sound, trust us!"?
"Hello, we are a serious cybersec firm and we have evaluated the code and here are our test with results that proof that we didn't find anything, the code is sound; Have we been through? We have, trust us!"
"Hello, we are a serious cybersec firm and we have evaluated the code and here are our test with results that proof that we didn't find anything, the code is sound; Have we been through? We have, trust us!"