Improve comments & readability in ClimbingStairs.java

[Hardvan]

The comment improvements for the ClimbingStairs class enhance clarity and adherence to Java documentation standards. The initial comment succinctly explains the problem and provides a detailed example of climbing combinations for five steps. The method-level comment for numberOfWays clearly outlines its purpose, input parameters, and return values, including special cases for n = 0 and n = 1. Inline comments within the method further clarify variable roles and loop logic, resulting in more readable and maintainable code.

• 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 52.31%. Comparing base (e6f597a) to head (09ce90f).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5498   +/-   ##
=========================================
  Coverage     52.31%   52.31%           
  Complexity     3260     3260           
=========================================
  Files           526      526           
  Lines         15205    15205           
  Branches       2892     2892           
=========================================
  Hits           7954     7954           
  Misses         6924     6924           
  Partials        327      327           

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