Implement reverse subtraction for InfRational and enhance tests

- Added manual implementations for reverse subtraction between Rational, InfRational, and i64 types.
- Enhanced the test suite for InfRational to cover various operations including addition, subtraction, multiplication, and division with both Rational and i64 types.
- Introduced tests for edge cases in the display of linear expressions and ensured consistent formatting.
- Added tests for the reciprocal method in the Rational struct, including edge cases for zero and infinity.
- Improved handling of AddAssign and SubAssign operations with infinity in the Rational struct.

Author: riccardodebenedictis