Converts the given number to a signed 8-bit integer (`int8`) by rounding to the nearest whole number and typecasting.
If the number exceeds the range of an `int8` (-128 to 127), it will wrap due to typecasting.
s8(value)
s8(10.7); // returns 11
s8(-129); // returns 127 (wrap)
s8(200); // returns -56 (wrap)