refactor: improve median calculator class design and readability

[alxkm]

Refactored the abstract class MedianOfRunningArray to improve clarity, extensibility, and maintainability.

Changes made:

• Renamed median() → getMedian() for clearer naming convention.
• Improved JavaDoc comments for class and methods to enhance code documentation and readability.
• Extracted heap balancing logic into a dedicated private method balanceHeapsIfNeeded() to reduce code duplication.
• Changed method access modifiers:
  • Made insert() and getMedian() final to prevent override and preserve consistency.
  • Changed heap fields to final.
• Added detailed exception message and @throws tag when median is requested on an empty data set.
• General formatting and naming improvements for consistency and readability.

• 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 code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.56%. Comparing base (8512f12) to head (1ae0ff9).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6349   +/-   ##
=========================================
  Coverage     74.55%   74.56%           
- Complexity     5452     5454    +2     
=========================================
  Files           682      682           
  Lines         19032    19033    +1     
  Branches       3689     3688    -1     
=========================================
+ Hits          14190    14192    +2     
  Misses         4278     4278           
+ Partials        564      563    -1     

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[siriak]

Looks good, thanks!