Optimize power() using exponentiation by squaring (O(log n))

[Vinayak-v12]

This PR optimizes the power() method by replacing the linear recursive
implementation with an exponentiation-by-squaring approach.

✔ Time complexity reduced from O(n) → O(log n)
✔ Handles negative exponents
✔ Keeps same behavior as original implementation
✔ Fully compatible with existing test cases
✔ No API changes

This improves performance and reduces recursion depth while maintaining clean readability.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.33%. Comparing base (a008cc2) to head (0537442).

Files with missing lines	Patch %	Lines
...a/com/thealgorithms/maths/PowerUsingRecursion.java	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7069   +/-   ##
=========================================
  Coverage     78.33%   78.33%           
- Complexity     6670     6672    +2     
=========================================
  Files           753      753           
  Lines         22185    22192    +7     
  Branches       4356     4359    +3     
=========================================
+ Hits          17378    17384    +6     
  Misses         4107     4107           
- Partials        700      701    +1     

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