Make stream info visible to users in describe (#7589)

Closes #7581.

After this PR, `describe` shows `(stream)` next to input that arrived at
`describe` as a `ListStream`:
```bash
〉ls | describe
table<name: string, type: string, size: filesize, modified: date> (stream)
〉[1 2 3] | each {|i| $i} | describe
list<int> (stream)
```

`describe` must collect all items of the stream to display type
information for lists and tables. If users need to avoid collecting
input, they can use the `-n`/`--no-collect` flag:

```bash
〉[1 2 3] | each {|i| $i} | describe --no-collect
stream
```

crates/nu-command/src/example_test.rs

@@ -13,7 +13,7 @@ mod test_examples {
         MathRound, Path, Random, Split, SplitColumn, SplitRow, Str, StrJoin, StrLength, StrReplace,
         Url, Values, Wrap,
     };
-    use crate::{Break, Mut, To};
+    use crate::{Break, Each, Mut, To};
     use itertools::Itertools;
     use nu_protocol::{
         ast::Block,
@@ -61,6 +61,7 @@ mod test_examples {
             // Base functions that are needed for testing
             // Try to keep this working set small to keep tests running as fast as possible
             let mut working_set = StateWorkingSet::new(&engine_state);
+            working_set.add_decl(Box::new(Each));
             working_set.add_decl(Box::new(Let));
             working_set.add_decl(Box::new(Str));
             working_set.add_decl(Box::new(StrJoin));