Warn on unnecessary unsafe blocks

[asterite]

Problem

Code like this:

fn main() {
    unsafe {
        foo();
    }
}

fn foo() {}

does not warn that the unsafe block is not needed. If the compiler does not tells us it's unneeded we could think the call is unsafe when it actually isn't.

Similarly, if there's unsafe nested inside another unsafe, the compiler should warn about it.

Happy Case

The compiler detects unsafe blocks that don't have any unconstrained calls, or unsafe blocks that happen inside unconstrained calls.

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

None

Blocker Context

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response