Apply nightly clippy lints (#9654)

# Description
- A new one is the removal of unnecessary `#` in raw strings without `"`
inside.
-
https://rust-lang.github.io/rust-clippy/master/index.html#/needless_raw_string_hashes
- The automatically applied removal of `.into_iter()` touched several
places where #9648 will change to the use of the record API. If
necessary I can remove them @IanManske to avoid churn with this PR.
- Manually applied `.try_fold` in two places
- Removed a dead `if`
- Manual: Combat rightward-drift with early return

crates/nu-cmd-lang/src/example_support.rs

@@ -188,8 +188,7 @@ pub fn check_all_signature_input_output_types_entries_have_examples(
     signature: Signature,
     witnessed_type_transformations: HashSet<(Type, Type)>,
 ) {
-    let declared_type_transformations =
-        HashSet::from_iter(signature.input_output_types.into_iter());
+    let declared_type_transformations = HashSet::from_iter(signature.input_output_types);
     assert!(
         witnessed_type_transformations.is_subset(&declared_type_transformations),
         "This should not be possible (bug in test): the type transformations \