ci: take integration tests into account for front coverage

[multun]

At first I thought it would be fairly easy to have consistent code coverage for e2e tests and unit tests, but it's not:

• unit tests are currently covered using v8's builtin code coverage, which is good, but does not work on all browsers. There is no build time instrumentation involved, just the js runtime doing the tracking.
• the only way I found to instrument e2e tests is using istanbul, which instruments code at compile time. unfortunately, it does so using babel, which struggles processing the already transpiled js from react-swc
• there's an swc plugin called swc-plugin-coverage-instrument which produces istanbul compatible instrumentation
• if this plugin were to be used, vitest's istanbul support would have to skip instrumentation

Base problem

The same coverage system has to be used for both e2e tests and unit tests, so codecov can properly merge reports

Use istanbul everywhere

• apply the instrumentation transform once, at the react swc stage (https://github.com/vitejs/vite-plugin-react-swc#plugins) using https://github.com/kwonoj/swc-plugin-coverage-instrument. Instrumented builds take a long time and do not yield good results, as babel is post-processing the output of swc
• patch vitest so it uses swc instrumentation / can rely on existing instrumentation feat: support istanbul coverage provider vitest-dev/vitest#1676 (comment)
• maybe fix feat(coveragevisitor): implement shouldignore kwonoj/swc-plugin-coverage-instrument#22

Pros:

• better, more consistent coverage results

Cons:

• complexity

Use v8 everywhere

This would only work on chrome, but is easier to get working, as it does not require build instrumentation

• change the existing code to use the playwright code coverage API

Pros:

• easier to get working

Cons:

• worse coverage results
• only works on chrome / node

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d075d80) 16.04% compared to head (2a773f6) 45.97%.

Additional details and impacted files

@@              Coverage Diff              @@
##                dev    #5976       +/-   ##
=============================================
+ Coverage     16.04%   45.97%   +29.93%     
  Complexity     2117     2117               
=============================================
  Files           780      729       -51     
  Lines        101927    24048    -77879     
  Branches       2665     4696     +2031     
=============================================
- Hits          16351    11057     -5294     
+ Misses        84003    12105    -71898     
+ Partials       1573      886      -687     

Flag	Coverage Δ
core	79.01% <ø> (ø)
front	19.35% <ø> (+10.92%)	⬆️
gateway	2.75% <ø> (ø)

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