Added rational number fuzzer functions and corresponding tests

[adrian052]

Functions Added:

1. rational: Generates a random rational value within the range of [-255; 16383].
2. rational_between: Generates rational values between specified bounds.
3. rational_at_least: Generates a random rational value with a lower bound constraint.
4. rational_at_most: Generates a random rational value with an upper bound constraint.

Note:
The current range for rational_between is set between -255 and 255. However, this range is flexible and could be adjusted based on any further requirements or suggestions.