docs: improve LinearSearch documentation with examples and step-by-step explanation

[07Vineet07]

Improved documentation for LinearSearch implementation as suggested in issue #7334.

Changes made:

• Added step-by-step explanation of how the algorithm works
• Added a concrete example with input/output
• Improved time complexity descriptions (best/average/worst case)
• Improved method-level Javadoc

Closes #7334

• 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.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.69%. Comparing base (e49cd55) to head (72cf3d3).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7435      +/-   ##
============================================
- Coverage     79.70%   79.69%   -0.02%     
+ Complexity     7275     7272       -3     
============================================
  Files           802      802              
  Lines         23700    23700              
  Branches       4661     4661              
============================================
- Hits          18891    18888       -3     
  Misses         4055     4055              
- Partials        754      757       +3     

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[DenizAltunkapan]

thank you for your contribution