test(dp): add tests for LongestPalindromicSubsequence and remove main…

[amangupta982]

Description

Added comprehensive test coverage for LongestPalindromicSubsequence and cleaned up the implementation:

• Added LongestPalindromicSubsequenceTest.java with 9 test cases covering empty string, single character, all same characters, already palindrome, null input, and structural correctness checks
• Removed main() method from implementation (not required per repo style)
• Added null check that actually throws IllegalArgumentException (was declared but never thrown)
• Replaced old-style length() == 0 with isEmpty()
• Simplified verbose if/else into ternary expression
• Improved Javadoc with @param, @return, and @throws

• 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 79.80%. Comparing base (d792409) to head (03fae68).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7462      +/-   ##
============================================
+ Coverage     79.72%   79.80%   +0.07%     
- Complexity     7298     7301       +3     
============================================
  Files           803      803              
  Lines         23762    23751      -11     
  Branches       4672     4671       -1     
============================================
+ Hits          18945    18954       +9     
+ Misses         4059     4036      -23     
- Partials        758      761       +3     

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[DenizAltunkapan]

@amangupta982 Thank you for your contribution