Add examples for math.gamma() and math.lgamma(

[vishnoi246]

Summary

Added practical examples for special math functions demonstrating:

• Standard use cases (integer/fractional inputs)
• Edge cases (negative values and poles)
• Error conditions
• Mathematical relationships between functions

Changes Made

1. Added examples showing math.gamma() behavior:

   >>> math.gamma(5)      # factorial(n-1) relationship
   24.0
   >>> math.gamma(0)      # pole behavior
   Traceback (most recent call last):
       ...
   ValueError: math domain error

math.lgamma(5) # log-gamma of factorial(4)
3.1780538303479458
math.lgamma(0) # pole behavior
Traceback (most recent call last):
...
ValueError: math domain error

---

📚 Documentation preview 📚: https://cpython-previews--137489.org.readthedocs.build/

[python-cla-bot]

The following commit authors need to sign the Contributor License Agreement:

• [email protected]