feat(theme): add 'gruvbox-material-dark-hard' theme

[G4bbix]

Description of change

A theme made by doing almost the exact thing as in #32. Except for using the gruvbox-material color pallet in dark, with hard contrast. https://github.com/sainnhe/gruvbox-material

How has this been tested?

Just looking at it

How has this been tested? (if applicable)

I just ran all the Tests and formatters describe in your CONTRIBUTING.md

[orhun]

Sick 🔥

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 27 lines in your changes missing coverage. Please review.

Project coverage is 7.36%. Comparing base (c82e882) to head (580ed9a).

Files with missing lines	Patch %	Lines
src/theme.rs	0.00%	27 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #77      +/-   ##
========================================
- Coverage   7.63%   7.36%   -0.27%     
========================================
  Files         13      13              
  Lines        747     774      +27     
========================================
  Hits          57      57              
- Misses       690     717      +27     

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