Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer. Key rules:

1. Whitespace: Ignore leading whitespace.
2. Signedness: Determine if the result is positive or negative based on '-' or '+'.
3. Conversion: Read characters until a non-digit character is encountered.
4. Rounding: If the integer is out of the 32-bit signed integer range, clamp it to INT_MIN or INT_MAX.

• A string s.

Input: s = " -42"
Output: -42