fix range semantic in detect_columns, str substring, str index-of (#12894)

# Description
Fixes: https://github.com/nushell/nushell/issues/7761

It's still unsure if we want to change the `range semantic` itself, but
it's good to keep range semantic consistent between nushell commands.

# User-Facing Changes
### Before
```nushell
❯ "abc" | str substring 1..=2
b
```
### After
```nushell
❯ "abc" | str substring 1..=2
bc
```

# Tests + Formatting
Adjust tests to fit new behavior

tests/repl/test_strings.rs

@@ -3,7 +3,7 @@ use crate::repl::tests::{fail_test, run_test, TestResult};
 #[test]
 fn cjk_in_substrings() -> TestResult {
     run_test(
-        r#"let s = '[Rust 程序设计语言](title-page.md)'; let start = ($s | str index-of '('); let end = ($s | str index-of ')'); $s | str substring ($start + 1)..($end)"#,
+        r#"let s = '[Rust 程序设计语言](title-page.md)'; let start = ($s | str index-of '('); let end = ($s | str index-of ')'); $s | str substring ($start + 1)..<($end)"#,
         "title-page.md",
     )
 }