Add an is_active function, and remove panic on not using

tests/inactive.rs

@@ -0,0 +1,4 @@
+#[test]
+fn is_inactive() {
+    assert!(!qadapt::is_active());
+}

tests/unused_panic.rs

@@ -1,11 +0,0 @@
-use qadapt::enter_protected;
-
-#[test]
-#[should_panic]
-fn guard_without_initialization() {
-    if cfg!(debug_assertions) {
-        enter_protected();
-    } else {
-        panic!("Intentional")
-    }
-}