refactor: simplify watchmap traversal (#98)

* refactor: use NonZeroU32 for literals
* refactor: watch traversal

src/internal/mod.rs

@@ -3,3 +3,6 @@ pub mod frozen_copy_map;
 pub mod id;
 pub mod mapping;
 pub mod small_vec;
+mod unwrap_unchecked;
+
+pub use unwrap_unchecked::debug_expect_unchecked;

src/internal/unwrap_unchecked.rs

@@ -0,0 +1,13 @@
+/// An unsafe method that unwraps an option without checking if it is `None` in
+/// release mode but does check the value in debug mode.
+#[track_caller]
+pub unsafe fn debug_expect_unchecked<T>(opt: Option<T>, _msg: &str) -> T {
+    #[cfg(debug_assertions)]
+    {
+        opt.expect(_msg)
+    }
+    #[cfg(not(debug_assertions))]
+    {
+        opt.unwrap_unchecked()
+    }
+}