Add tests, remove main, improve docs in ExponentialSearch

[Hardvan]

• 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.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 60.87%. Comparing base (a4e4319) to head (8277982).

Files with missing lines	Patch %	Lines
...a/com/thealgorithms/searches/ExponentalSearch.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5664      +/-   ##
============================================
+ Coverage     60.78%   60.87%   +0.09%     
  Complexity     3910     3910              
============================================
  Files           563      563              
  Lines         16026    16017       -9     
  Branches       3075     3075              
============================================
+ Hits           9742     9751       +9     
+ Misses         5876     5857      -19     
- Partials        408      409       +1     

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