fix 64-bit hex number parsing (nushell#14571)

# Description

Closes nushell#14521 

This PR tweaks the way 64-bit hex numbers are parsed.

### Before
```nushell
❯ 0xffffffffffffffef
Error: nu::shell::external_command

  × External command failed
   ╭─[entry nushell#1:1:1]
 1 │ 0xffffffffffffffef
   · ─────────┬────────
   ·          ╰── Command `0xffffffffffffffef` not found
   ╰────
  help: `0xffffffffffffffef` is neither a Nushell built-in or a known external command
```

### After
```nushell
❯ 0xffffffffffffffef
-17
```

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crates/nu-parser/src/parser.rs

@@ -1532,7 +1532,9 @@ pub fn parse_int(working_set: &mut StateWorkingSet, span: Span) -> Expression {
         span: Span,
         radix: u32,
     ) -> Expression {
-        if let Ok(num) = i64::from_str_radix(token, radix) {
+        // Parse as a u64, then cast to i64, otherwise, for numbers like "0xffffffffffffffef",
+        // you'll get `Error parsing hex string: number too large to fit in target type`.
+        if let Ok(num) = u64::from_str_radix(token, radix).map(|val| val as i64) {
             Expression::new(working_set, Expr::Int(num), span, Type::Int)
         } else {
             working_set.error(ParseError::InvalidLiteral(