feat(slidingwindow): add SmallestSubarrayWithSum algorithm

[nihalsingh373]

Added a new algorithm SmallestSubarrayWithSum in the slidingwindow package.
It finds the minimum length subarray with sum ≥ target using the sliding window technique.
Runs in O(n) time and O(1) space.
Handles edge cases like empty arrays and single-element subarrays.
Implements clean, modular, and documented code per Checkstyle rules.
Follows TheAlgorithms Java contribution standards.
Enhances the collection of sliding window algorithms.
Useful for interview prep and competitive programming.
Validated locally with mvn checkstyle:check — no style errors.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.35%. Comparing base (bb6385e) to head (2d7a451).

Files with missing lines	Patch %	Lines
...orithms/slidingwindow/SmallestSubarrayWithSum.java	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6986      +/-   ##
============================================
- Coverage     78.35%   78.35%   -0.01%     
- Complexity     6615     6619       +4     
============================================
  Files           746      747       +1     
  Lines         22015    22024       +9     
  Branches       4320     4323       +3     
============================================
+ Hits          17249    17256       +7     
- Misses         4078     4079       +1     
- Partials        688      689       +1     

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[nihalsingh373]

Hi maintainers 👋

All CI and Checkstyle checks have successfully passed ✅
This PR adds the SmallestSubarrayWithSum algorithm under the slidingwindow package, following the project’s coding and documentation guidelines.

Kindly review when convenient — I’d appreciate your feedback or approval for merge 🙌

Thanks for maintaining this amazing project! 💡