finish current clippy lints to make CI green

src/c_str.rs

@@ -258,6 +258,7 @@ impl<'a, T: Kind> NulStr<'a, T> {
     /// Scan the string to get its length.
     #[doc(alias = "strlen")]
     #[doc(alias = "wcslen")]
+    #[expect(clippy::len_without_is_empty, reason = "len() signature intentional")]
     pub fn len(self) -> usize {
         self.to_chars().len()
     }

src/macros.rs

@@ -117,6 +117,7 @@ macro_rules! trace_expr {
 
 // log::trace! but functions inside them will
 // not be evaluated or compiled unless enabled
+#[cfg(target_os = "redox")] // currently only used in redox
 macro_rules! trace_log {
     ($($arg:tt)+) => {
         #[cfg(not(feature = "no_trace"))]