feat: track theme file md5 hash

[ReenigneArcher]

Description

Begin tracking the md5 hash of a file, so we can determine if a theme is supplied by Themerr. This is a prerequisite for adding a dashboard report.

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[codecov]

Codecov Report

Merging #185 (9a8ad76) into master (eddfed8) will increase coverage by 8.91%.
The diff coverage is 66.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
+ Coverage   38.88%   47.80%   +8.91%     
==========================================
  Files           4        4              
  Lines         198      228      +30     
  Branches       11       16       +5     
==========================================
+ Hits           77      109      +32     
+ Misses        117      115       -2     
  Partials        4        4              

Files	Coverage Δ
Jellyfin.Plugin.Themerr/ThemerrManager.cs	61.93% <66.66%> (+9.19%)	⬆️