Ignoring warnings is really not a good way to deal with it. If a compiler is bitching about something there is a reason to.
A lot of times the devs are too overworked or a little underloaded in the supply of fucks to give, so they ignore them.
In some really high quality codebases, they turn on "treat warnings as errors" to ensure better code.
No there is not. Borrow checking and RAII existed in C++ too and there is no formal axiomatic proof of their safety in a general sense. Only to a very clearly defined degree.
In fact, someone found memory bugs in Rust, again, because it is NOT soundly memory safe.
Dart is soundly Null-safe. Meaning it can never mathematically compile null unsafe code unless you explicitly say you're OK with it. Kotlin is simply Null safe, meaning it can run into bullshit null conditions.
The same thing with Rust: don't let it lull you into a sense of security that doesn't exist.