Changes proposed in this pull request:

• fractional() produced a doubled negative sign for negative mixed numbers. fractional(-1.3) returned '-1 -3/10' instead of '-1 3/10', and fractional(-2.5) returned '-2 -1/2'. The whole-number part already carries the sign (int(-1.3) == -1), so repeating it on the numerator is wrong. This is inconsistent with the pure-fraction case, which is already correct (fractional(-0.3) == '-3/10').
• Fix: use abs(numerator) in the mixed-fraction output. Positives and pure fractions are unaffected.
• Add regression cases (-0.3, -1.3, -2.5) to the parametrized test_fractional — it previously had no negative inputs. Verified the new cases fail on the current code and pass with the fix; the full tests/test_number.py suite (222 tests) passes and ruff is clean.

No existing issue.