Clippy fixes from stable and nightly (#13455)

- **Doccomment style fixes**
- **Forgotten stuff in `nu-pretty-hex`**
- **Don't `for` around an `Option`**
- and more

I think the suggestions here are a net positive, some of the suggestions
moved into #13498 feel somewhat arbitrary, I also raised
https://github.com/rust-lang/rust-clippy/issues/13188 as the nightly
`byte_char_slices` would require either a global allow or otherwise a
ton of granular allows or possibly confusing bytestring literals.

crates/nu-protocol/src/pipeline/pipeline_data.rs

@@ -19,12 +19,12 @@ const LINE_ENDING_PATTERN: &[char] = &['\r', '\n'];
 /// We've tried a few variations of this structure. Listing these below so we have a record.
 ///
 /// * We tried always assuming a stream in Nushell. This was a great 80% solution, but it had some rough edges.
-/// Namely, how do you know the difference between a single string and a list of one string. How do you know
-/// when to flatten the data given to you from a data source into the stream or to keep it as an unflattened
-/// list?
+///   Namely, how do you know the difference between a single string and a list of one string. How do you know
+///   when to flatten the data given to you from a data source into the stream or to keep it as an unflattened
+///   list?
 ///
 /// * We tried putting the stream into Value. This had some interesting properties as now commands "just worked
-/// on values", but lead to a few unfortunate issues.
+///   on values", but lead to a few unfortunate issues.
 ///
 /// The first is that you can't easily clone Values in a way that felt largely immutable. For example, if
 /// you cloned a Value which contained a stream, and in one variable drained some part of it, then the second
@@ -37,8 +37,8 @@ const LINE_ENDING_PATTERN: &[char] = &['\r', '\n'];
 /// concrete list values rather than streams, and be able to view them without non-local effects.
 ///
 /// * A balance of the two approaches is what we've landed on: Values are thread-safe to pass, and we can stream
-/// them into any sources. Streams are still available to model the infinite streams approach of original
-/// Nushell.
+///   them into any sources. Streams are still available to model the infinite streams approach of original
+///   Nushell.
 #[derive(Debug)]
 pub enum PipelineData {
     Empty,