Enable Unwind Attribute from Parsing metadata files

[jaisnan]

Requested feature:

We are writing the unwind values into the metadata files. We should now read form these metadata files to use them as attributes fully.

This is a follow up of - #846.

Use case:

Enable the unwind attribute.

Test case:

#[kani::proof]
#[kani::unwind(10)]
fn harness() {
    let mut counter = 0;
    loop {
        counter += 1;
        assert!(counter < 10);
    }
}