prevent crash when use redirection with let/mut (#10139)

Fix #9992 

I mistakenly messed up https://github.com/nushell/nushell/pull/10118 and
this is a cleaned version.

# Description

* This pr changes the panic to errors while parsing `let`, now user will
get the following errors:
<img width="395" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/4b39ac14-cd1f-47b3-9490-81009ca42717">
<img width="394" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/71ce33ad-f4d0-4132-828f-9674b9603556">
<img width="440" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/257eab4d-1a72-42db-b09e-f42bef33d2ec">

* `out+err>` is cached by `parse_expression` but not this, which may be
a potential problem.
* `Commond(None, ..)` remains panic for future bug report because I
don't actually know when/how does it happen

# User-Facing Changes

Nushell won't crash when user typing `let a = 1 err> ...`

# Tests + Formatting

- `cargo fmt --all -- --check` : OK
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` : OK
- `cargo test --workspace` : OK
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` : OK

# After Submitting

None

Co-authored-by: Horasal <horsal@horsal.dev>

crates/nu-parser/src/parser.rs

@@ -5439,6 +5439,17 @@ pub fn parse_pipeline(
                                 new_command.comments.extend_from_slice(&command.comments);
                                 new_command.parts.extend_from_slice(&command.parts);
                             }
+                            LiteElement::Redirection(span, ..) => {
+                                working_set.error(ParseError::RedirectionInLetMut(*span, None))
+                            }
+                            LiteElement::SeparateRedirection { out, err } => {
+                                working_set.error(ParseError::RedirectionInLetMut(
+                                    out.0.min(err.0),
+                                    Some(out.0.max(err.0)),
+                                ))
+                            }
+                            LiteElement::SameTargetRedirection { redirection, .. } => working_set
+                                .error(ParseError::RedirectionInLetMut(redirection.0, None)),
                             _ => panic!("unsupported"),
                         }
                     }