docs: add Javadoc to FibonacciSeries

[singhc7]

Description

Converted the standard block comments in FibonacciSeries.java to formal Javadoc. This ensures that IDEs like IntelliJ properly display documentation when hovering over the class or methods.

Changes

• Added @param and @return tags to the fibonacci method.

• Formatted the class-level documentation with usage examples.

• 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.05%. Comparing base (782d075) to head (d0cb7bb).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7215   +/-   ##
=========================================
  Coverage     79.05%   79.05%           
- Complexity     6944     6945    +1     
=========================================
  Files           779      779           
  Lines         22906    22906           
  Branches       4502     4502           
=========================================
+ Hits          18108    18109    +1     
  Misses         4077     4077           
+ Partials        721      720    -1     

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