let and mut panic if tokens are placed after a redirection

[1Kinoti]

Describe the bug

let and mut should look like this

let foo = 42
mut bar = 69

If a redirection is placed between the variable name and =, attempting to add another token panics nu

This also happens even if there are type annotations

let foo: int = 42

How to reproduce

1. Write this in your repl

let foo = 42
# or
mut bar = 69

2. Move the cursor to anywhere between the variable name and the =

let foo = 42
#      ^
#      |
#      move the cursor here

3. Add any redirection in the cursor position

let foo o> file.nu = 42
#          -------
#             |
#             immediately after writing 'f', nu panics

Expected behavior

1. Not panic()!
2. Accept the redirection keyword and the target, and reject them gracefully later

Configuration

key	value
version	0.97.1
major	0
minor	97
patch	1
branch
commit_hash	60769ac
build_os	linux-x86_64
build_target	x86_64-unknown-linux-gnu
rust_version	rustc 1.78.0 (9b00956e5 2024-04-29)
rust_channel	1.78.0-x86_64-unknown-linux-gnu
cargo_version	cargo 1.78.0 (54d8815d0 2024-03-26)
build_time	2024-08-21 03:29:24 +00:00
build_rust_channel	release
allocator	mimalloc
features	default, sqlite, static-link-openssl, system-clipboard, trash
installed_plugins

Panic message

let foo o> Error:   × Main thread panicked.
  ├─▶ at crates/nu-protocol/src/engine/state_working_set.rs:385:48
  ╰─▶ slice index starts at 15 but ends at 12
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.

[KAAtheWiseGit]

This happens even if you type normally, right at the = character. This is what I get at 5101b5e:

~/fork/nushell> let foo o> file Error:   × Main thread panicked.
  ├─▶ at crates/nu-protocol/src/span.rs:187:9
  ╰─▶ assertion failed: spans.windows(2).all(|spans|
              {
                  let &[a, b] = spans else { return false; };
                  a.start <= b.start && a.end <= b.end
              })
         0: 0x564874f1ad54 - rust_begin_unwind
         1: 0x5648719ec063 - core::panicking::panic_fmt::h556dd313afe3d53e
         2: 0x5648719ec0ec - core::panicking::panic::hac5d0741b9be4a00
         3: 0x5648745a84b0 - nu_protocol::span::Span::concat::h27e6cc6003258db3
                      at /home/kaathewise/fork/nushell/crates/nu-protocol/src/span.rs:187
         4: 0x56487369b5d1 - nu_parser::parse_keywords::parse_let::h942bf08e8d5b2400
                      at /home/kaathewise/fork/nushell/crates/nu-parser/src/parse_keywords.rs:3127
         5: 0x56487370b1a3 - nu_parser::parser::parse_builtin_commands::h0f93e1158d050920
                      at /home/kaathewise/fork/nushell/crates/nu-parser/src/parser.rs:5598
         6: 0x56487370f1e4 - nu_parser::parser::parse_pipeline::h404fb07b7bd0b3a4
                      at /home/kaathewise/fork/nushell/crates/nu-parser/src/parser.rs:5983
         7: 0x56487370f853 - nu_parser::parser::parse_block::h3a794479b0a7fa59
                      at /home/kaathewise/fork/nushell/crates/nu-parser/src/parser.rs:6017
         8: 0x5648737149b1 - nu_parser::parser::parse::h8625e6639ecf9fcf
                      at /home/kaathewise/fork/nushell/crates/nu-parser/src/parser.rs:6565
         9: 0x56487330a1a5 - <nu_cli::syntax_highlight::NuHighlighter as reedline::highlighter::Highlighter>::highlight::h5b073a4b913cb1f8
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/syntax_highlight.rs:26
        10: 0x56487343080a - reedline::engine::Reedline::buffer_paint::hf271607f81f8033a
                      at /home/kaathewise/.local/state/cargo/git/checkouts/reedline-e42026a78d91c510/7af8959/src/engine.rs:1740
        11: 0x56487342d90b - reedline::engine::Reedline::repaint::hb35f6d4ec72e4c1c
                      at /home/kaathewise/.local/state/cargo/git/checkouts/reedline-e42026a78d91c510/7af8959/src/engine.rs:1505
        12: 0x564873426df9 - reedline::engine::Reedline::read_line_helper::hf0ab89bce4d8be63
                      at /home/kaathewise/.local/state/cargo/git/checkouts/reedline-e42026a78d91c510/7af8959/src/engine.rs:802
        13: 0x564873426120 - reedline::engine::Reedline::read_line::h5b125cba9094a8b8
                      at /home/kaathewise/.local/state/cargo/git/checkouts/reedline-e42026a78d91c510/7af8959/src/engine.rs:646
        14: 0x5648732b55ad - nu_cli::repl::loop_iteration::h6816b17367ca997b
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:450
        15: 0x5648732a1b82 - nu_cli::repl::evaluate_repl::{{closure}}::hbca2bfde76009799
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:190
        16: 0x56487325cccf - <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::h895fb711eb7591ef
                      at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/core/src/panic/unwind_safe.rs:272
        17: 0x5648732ea4a0 - std::panicking::try::do_call::h1cf869321e89d99f
                      at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/std/src/panicking.rs:557
        18: 0x5648732d3c2b - __rust_try
        19: 0x5648732d3b6e - std::panicking::try::hc4b39dbf45d3d1c2
                      at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/std/src/panicking.rs:521
                       - std::panic::catch_unwind::he3bf7de7bdf452cc
                      at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/std/src/panic.rs:350
        20: 0x5648732ae5aa - nu_cli::repl::evaluate_repl::h65b3e40271ec5dc4
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:189
        21: 0x564871a4fc28 - nu::run::run_repl::he4323f7bae4513ca
                      at /home/kaathewise/fork/nushell/src/run.rs:208
        22: 0x564871a02fa9 - nu::main::ha6e44a0e5fd8878b
                      at /home/kaathewise/fork/nushell/src/main.rs:416
        23: 0x564871a51d1b - core::ops::function::FnOnce::call_once::hd3df071a50ca3844
                      at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/core/src/ops/function.rs:250
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.