Optimize sieveOfEratosthenes: reduced memory usage and iterations

[Sumit210106]

• Mark only odd multiples starting from i² to reduce iterations
• Collect primes after marking to avoid duplicates and simplify logic
• Explicitly include 2 and skip even numbers throughout

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Describe your change:

• Optimize an existing algorithm (sieveOfEratosthenes)

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file (sieveOfEratosthenes.js).
• All filenames follow UpperCamelCase (PascalCase) style.
• The algorithm has a URL in its comments pointing to Wikipedia.
• (Optional) If this PR fixes an open issue, I have added Fixes: #ISSUE_NO in the commit message.

Summary of Improvements

• Reduced memory usage by ~50% by skipping even numbers (except 2).
• Reduced number of iterations:
  • Outer loop increments by 2 (odd-only).
  • Inner loop starts from i*i and marks only odd multiples (j += 2*i).
• Same time complexity O(n log log n) but with a smaller constant factor → faster in practice.
• Added clearer inline comments in the code for maintainability.

Example

sieveOfEratosthenes(20)
// Output: [2, 3, 5, 7, 11, 13, 17, 19]

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.92%. Comparing base (08d8c6b) to head (33af5aa).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1813   +/-   ##
=======================================
  Coverage   85.91%   85.92%           
=======================================
  Files         379      379           
  Lines       19778    19789   +11     
  Branches     3015     3022    +7     
=======================================
+ Hits        16993    17004   +11     
  Misses       2785     2785           

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