feat: add QuadraticEquationSolver and test cases

[sailok]

• 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 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 58.14%. Comparing base (5dcf6c0) to head (d45551f).

Files with missing lines	Patch %	Lines
...m/thealgorithms/maths/QuadraticEquationSolver.java	89.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5619      +/-   ##
============================================
+ Coverage     58.11%   58.14%   +0.02%     
- Complexity     3676     3679       +3     
============================================
  Files           546      547       +1     
  Lines         15796    15815      +19     
  Branches       3006     3009       +3     
============================================
+ Hits           9180     9195      +15     
- Misses         6225     6227       +2     
- Partials        391      393       +2     

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[siriak]

Looks good, thanks!