use `.iter().{any,all}` instead of manual iteration

and also fix a bug in the logic because of that.

rust/solve/src/dpll.rs

/// A satisfied clause is a clause where at least one atom is true.
fn is_clause_satisfied(vars: &BoundVars, clause: Clause) -> bool {
    for v in clause {
        if is_true(vars, v) {
            return true
        }
    }
    
    return false
    clause.iter().any(|v| is_true(vars, *v))
}
#[test]
/// A conflict clause is a clause whose atoms each are false.
fn is_clause_conflict(vars: &BoundVars, clause: Clause) -> bool {
    for v in clause {
        if is_true(vars, v) {
            return false
        }
    }
    return true
    clause.iter().all(|v| is_false(vars, *v))
}
#[test]
fn test_is_clause_conflict() {
    assert!(is_clause_conflict(&empty_vars(), vec!(1)));
    assert!(is_clause_conflict(&empty_vars(), vec!(1, 2, 3)));
    assert!(is_clause_conflict(&from_vec(vec!(4)), vec!(1, 2, 3)));
    assert!(is_clause_conflict(&from_vec(vec!(-1)), vec!(1)));
    assert!(is_clause_conflict(&from_vec(vec!(-1, -2, -3)), vec!(1, 2, 3)));
    assert!(is_clause_conflict(&from_vec(vec!(-1, -2, -3, 4)), vec!(1, 2, 3)));
    assert!(!is_clause_conflict(&from_vec(vec!(1)), vec!(1)));
    assert!(!is_clause_conflict(&from_vec(vec!(2)), vec!(1, 2)));
}