Function isAlphabetic

isAlphabetic(value: string): boolean
Checks if a string contains only alphabetic characters (A–Z, a–z).
Parameters
- value: string
  The string to check.
Returns boolean
- true if the string contains only letters; otherwise, false.
Example
```
isAlphabetic("Hello"); // true
isAlphabetic("world123"); // false
isAlphabetic("Test!"); // false
```
- Defined in src/string/validate.ts:127