ListStream touchup (#12524)

# Description

Does some misc changes to `ListStream`:
- Moves it into its own module/file separate from `RawStream`.
- `ListStream`s now have an associated `Span`.
- This required changes to `ListStreamInfo` in `nu-plugin`. Note sure if
this is a breaking change for the plugin protocol.
- Hides the internals of `ListStream` but also adds a few more methods.
- This includes two functions to more easily alter a stream (these take
a `ListStream` and return a `ListStream` instead of having to go through
the whole `into_pipeline_data(..)` route).
  -  `map`: takes a `FnMut(Value) -> Value`
  - `modify`: takes a function to modify the inner stream.

crates/nu-command/src/generators/generate.rs

@@ -183,7 +183,7 @@ used as the next argument to the closure, otherwise generation stops.
 
         Ok(iter
             .flatten()
-            .into_pipeline_data(engine_state.ctrlc.clone()))
+            .into_pipeline_data(call.head, engine_state.ctrlc.clone()))
     }
 }
 

crates/nu-command/src/generators/seq.rs

@@ -1,4 +1,5 @@
 use nu_engine::command_prelude::*;
+use nu_protocol::ListStream;
 
 #[derive(Clone)]
 pub struct Seq;
@@ -119,36 +120,32 @@ pub fn run_seq(
     let step = if free.len() > 2 { free[1] } else { 1.0 };
     let last = { free[free.len() - 1] };
 
-    if !contains_decimals {
-        // integers only
-        Ok(PipelineData::ListStream(
-            nu_protocol::ListStream::from_stream(
-                IntSeq {
-                    count: first as i64,
-                    step: step as i64,
-                    last: last as i64,
-                    span,
-                },
-                engine_state.ctrlc.clone(),
-            ),
-            None,
-        ))
+    let stream = if !contains_decimals {
+        ListStream::new(
+            IntSeq {
+                count: first as i64,
+                step: step as i64,
+                last: last as i64,
+                span,
+            },
+            span,
+            engine_state.ctrlc.clone(),
+        )
     } else {
-        // floats
-        Ok(PipelineData::ListStream(
-            nu_protocol::ListStream::from_stream(
-                FloatSeq {
-                    first,
-                    step,
-                    last,
-                    index: 0,
-                    span,
-                },
-                engine_state.ctrlc.clone(),
-            ),
-            None,
-        ))
-    }
+        ListStream::new(
+            FloatSeq {
+                first,
+                step,
+                last,
+                index: 0,
+                span,
+            },
+            span,
+            engine_state.ctrlc.clone(),
+        )
+    };
+
+    Ok(stream.into())
 }
 
 struct FloatSeq {