MudRating: make HandleKeyDown async Task

[ScarletKuro]

Description

Follow up for #8877

I missed it since I thought the HandleKeyDown is done via key interceptor therefore it cannot be a Task for now, but it's coming from onkeydown.

How Has This Been Tested?

Visually

Type of Changes

• 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)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.20%. Comparing base (28bc599) to head (6de7fc4).
Report is 149 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8883      +/-   ##
==========================================
+ Coverage   89.82%   90.20%   +0.37%     
==========================================
  Files         412      423      +11     
  Lines       11878    12274     +396     
  Branches     2364     2407      +43     
==========================================
+ Hits        10670    11072     +402     
+ Misses        681      668      -13     
- Partials      527      534       +7     

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[ScarletKuro]

Will fix some stale comp.FindAll I see in tests and open it back, it's not necessary but to not come back to it just in case it will matter one day.
Btw, there is apparently enableAutoRefresh (default false) overload in FindAll("li", enableAutoRefresh: true); but I guess using lambda is just easier and we already started this function practice.

[ScarletKuro]

ready