DOC: Improve examples in Series.str.isnumeric shared docstring to include decimal, fraction, negatives and exponents (#60750)
- [x] closes #60750 
- [x] All [code checks passed](https://pandas.pydata.org/docs/dev/development/contributing_documentation.html#previewing-changes)
- [x] Validated changes for formatting issues using `scripts/validate_docstrings.py`

### Tasks performed

1.  Improved the existing example for `Series.str.isnumeric` to include Unicode fractions using shared docs.

2. Add a new example to clear confusion regarding decimals, exponents and negative values

### Before
![image](https://github.com/user-attachments/assets/e599b678-2736-4200-8e01-21445e5b59de)


### After 
![image](https://github.com/user-attachments/assets/c6180846-de53-4058-829d-5fb7da8c58a3)





Thanks @akj2018 