[ICE] Prusti panics when verifying closures that capture environment variables.

[rikki322]

Prusti consistently crashes with an Internal Compiler Error (ICE) when verifying any function containing a closure that captures variables from the enclosing scope (e.g., function arguments).
Reproduction

fn test(x: u64, y: u64) -> u64 {
    (|| {
    x / y 
})()
}
fn main() {
    test(1, 0);
}

Actual Behavior
The compiler panics with an internal error:

error: [Prusti: internal error] Prusti encountered an unexpected internal error
...
thread 'rustc' panicked at ...

Expected Behavior
Prusti should report a standard verification error, not crash.