infra: use vitest config

[Shinigami92]

this is just a minimal change to the vitest config
instead of using a vite config with /// <reference types="vitest" /> we use a vitest.config directly

because we do not use vite to bundle our project, but esbuild (or tsup in the future) there is no need to have a vite.config

https://vitest.dev/config/#configuration

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ca50f82) 99.57% compared to head (faca2c8) 99.57%.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #2612      +/-   ##
==========================================
- Coverage   99.57%   99.57%   -0.01%     
==========================================
  Files        2807     2807              
  Lines      250452   250452              
  Branches     1152     1148       -4     
==========================================
- Hits       249392   249379      -13     
- Misses       1032     1045      +13     
  Partials       28       28              

see 1 file with indirect coverage changes