feat(maths): enhance Average with stream method and improved JavaDoc

[Papichardog]

Description

Enhanced the Average.java utility class in the com.thealgorithms.maths package with two improvements:

• Improved JavaDoc comments on existing methods, clarifying truncation behavior on average(int[]) and adding @throws documentation.
• Added a new averageStream(double[]) method using the Java Stream API as a modern, declarative alternative. Returns OptionalDouble following Stream API conventions.

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.50%. Comparing base (e0a7223) to head (765d5d2).

Files with missing lines	Patch %	Lines
src/main/java/com/thealgorithms/maths/Average.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7369      +/-   ##
============================================
- Coverage     79.52%   79.50%   -0.02%     
  Complexity     7143     7143              
============================================
  Files           796      796              
  Lines         23365    23368       +3     
  Branches       4596     4596              
============================================
- Hits          18581    18579       -2     
- Misses         4047     4050       +3     
- Partials        737      739       +2     

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