Allow operator in constants (#10212)

This pr fixes https://github.com/nushell/nushell/issues/10200

# Description

Allow unary and binary operators in constants, e.g.

```bash
const a = 1 + 2
const b = [0, 1, 2, 3] ++ [4]
```

# User-Facing Changes

Now constants can contain operators.

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

None

---------

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

crates/nu-engine/src/eval.rs

@@ -2,8 +2,8 @@ use crate::{current_dir_str, get_full_help};
 use nu_path::expand_path_with;
 use nu_protocol::{
     ast::{
-        Argument, Assignment, Bits, Block, Boolean, Call, Comparison, Expr, Expression, Math,
-        Operator, PathMember, PipelineElement, Redirection,
+        eval_operator, Argument, Assignment, Bits, Block, Boolean, Call, Comparison, Expr,
+        Expression, Math, Operator, PathMember, PipelineElement, Redirection,
     },
     engine::{EngineState, ProfilingConfig, Stack},
     record, DataSource, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
@@ -13,19 +13,6 @@ use nu_protocol::{
 use std::collections::HashMap;
 use std::time::Instant;
 
-pub fn eval_operator(op: &Expression) -> Result<Operator, ShellError> {
-    match op {
-        Expression {
-            expr: Expr::Operator(operator),
-            ..
-        } => Ok(operator.clone()),
-        Expression { span, expr, .. } => Err(ShellError::UnknownOperator {
-            op_token: format!("{expr:?}"),
-            span: *span,
-        }),
-    }
-}
-
 pub fn eval_call(
     engine_state: &EngineState,
     caller_stack: &mut Stack,

crates/nu-engine/src/lib.rs

@@ -12,6 +12,6 @@ pub use documentation::get_full_help;
 pub use env::*;
 pub use eval::{
     eval_block, eval_block_with_early_return, eval_call, eval_expression,
-    eval_expression_with_input, eval_operator, eval_subexpression, eval_variable, redirect_env,
+    eval_expression_with_input, eval_subexpression, eval_variable, redirect_env,
 };
 pub use glob_from::glob_from;