Remove vitest single thread config

[blurfx]

What this PR does / why we need it?

Let vitest use multi threads to reduce the time it takes.

The test took about 20% less time(~90s to ~70s) in my local environment.

Any background context you want to provide?

What are the relevant tickets?

Fixes #654 #665

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c4938f7) 71.38% compared to head (9cfe1be) 67.83%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #667      +/-   ##
==========================================
- Coverage   71.38%   67.83%   -3.55%     
==========================================
  Files          58       58              
  Lines        8734     8734              
  Branches      784      784              
==========================================
- Hits         6235     5925     -310     
- Misses       2241     2550     +309     
- Partials      258      259       +1     

see 3 files with indirect coverage changes

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[blurfx]

It's slower in actions test environment.. 🤔

[hackerwins]

It took only 8s in my local environment.

Before:

After:

[hackerwins]

Thanks for your contribution.