Improve documentation for Linear Search algorithm

[SwaatiR]

This pull request improves the JavaDoc and formatting for the Linear Search
algorithm to make the explanation clearer and easier for beginners to understand.

No changes were made to the algorithm logic.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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  Coverage          ?   79.05%           
  Complexity        ?     6945           
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  Files             ?      779           
  Lines             ?    22906           
  Branches          ?     4502           
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  Hits              ?    18109           
  Misses            ?     4077           
  Partials          ?      720           

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