Fixed handling of trait methods containing the unsafe attribute

[PuffyWithEyes]

Currently, the application is throwing an error:

WARN: couldn't parse unsafe() attribute
WARN: Skipping dummy::DummyStruct::dummy - (not `no_mangle`, and has no `export_name` attribute)

In the following example:

struct DummyStruct {
    dummy: i32,
}

impl DummyStruct {
    #[unsafe(export_name = "new")]
    pub extern "C" dummy() -> Self {
        Self {
            dummy: 0,
        }
    }
}

Accordingly, the function new will not be generated in the header file. My solution fixes this error. Now, similar methods will not encounter this issue.

[emilio]

Could you add a test please?

[PuffyWithEyes]

@emilio yes, I can write

[PuffyWithEyes]

@emilio done. I hope I did everything right :)

[emilio]

Thank you!

[lpraneis]

Is there anything blocking this merge? I believe this will be required for Rust 2024 Edition updates since unsafe(no_mangle) is now required