Find middle linkedList

[Chintha-vardhan]

Fixes #6615
Implemented Find Middle of a Singly Linked List algorithm with unit tests

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.07%. Comparing base (c0ca704) to head (cf42d40).

Files with missing lines	Patch %	Lines
.../com/thealgorithms/LinkedList/TortoiseAndHare.java	0.00%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6737      +/-   ##
============================================
- Coverage     77.10%   77.07%   -0.04%     
- Complexity     6110     6111       +1     
============================================
  Files           719      720       +1     
  Lines         20437    20449      +12     
  Branches       3952     3954       +2     
============================================
+ Hits          15758    15761       +3     
- Misses         4080     4091      +11     
+ Partials        599      597       -2     

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