Fix: Correct HashMap size tracking and refactor LinkedList methods

[Born-as-Harsha]

{O}(1)$ Size Tracking and Encapsulation RefinementThis PR implements a critical fix for size tracking and refactors internal methods for improved efficiency and compliance with Java encapsulation principles in the HashMap data structure.🐛 Problem SolvedThe original HashMap.size() method was incorrect, as it returned the count of non-empty buckets (the array indices) instead of the total number of key-value entries stored across all linked lists. This resulted in the size being misreported whenever hash collisions occurred.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.52%. Comparing base (a14e1e3) to head (324e8f2).

Files with missing lines	Patch %	Lines
...rithms/datastructures/hashmap/hashing/HashMap.java	93.75%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7137   +/-   ##
=========================================
  Coverage     78.51%   78.52%           
+ Complexity     6752     6751    -1     
=========================================
  Files           759      759           
  Lines         22402    22409    +7     
  Branches       4400     4400           
=========================================
+ Hits          17589    17596    +7     
  Misses         4108     4108           
  Partials        705      705           

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