fix(fetch): end span after body is received

[mhennoch]

Which problem is this PR solving?

Currently fetch span end is called when fetch().then fires and 300ms wait time(for resource timings) is over. But fetch() promise resolves as soon as the server responds with headers so if getting the body takes more than 300ms there will never be any resource timings for this span and span end time will be incorrect also. To reproduce it just make a fetch and set connection speed slow in dev tools and you can see that none of the fetches have resource timings.

Short description of the changes

I clone the response and read the response body until it is done and end the span then. Not a pretty solution but this covers all of the cases I know about. Another potential way to fix this would be to wrap all body methods (.json .blob etc.) but that still leaves some use cases uncovered. Some changes to tests so done isn't called too early (took a looong time to get them stable). Also fixed some TS warnings in tests. Probably could get rid of the 300ms timeout now but I am not yet bold enough.

[codecov]

Codecov Report

Merging #2203 (afcbdd6) into main (e379e59) will decrease coverage by 0.01%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##             main    #2203      +/-   ##
==========================================
- Coverage   92.72%   92.71%   -0.02%     
==========================================
  Files         141      141              
  Lines        5089     5106      +17     
  Branches     1047     1049       +2     
==========================================
+ Hits         4719     4734      +15     
- Misses        370      372       +2     

Impacted Files	Coverage Δ
...s/opentelemetry-instrumentation-fetch/src/fetch.ts	96.98% <87.50%> (-1.67%)	⬇️
...emetry-core/src/platform/node/RandomIdGenerator.ts	93.75% <0.00%> (+6.25%)	⬆️

[obecny]

this is really nice finding, thx for fixes, lgtm, just some name change suggestions

[johnbley]

+1

[mhennoch]

@dyladan @vmarchaud Can I get one more review and if possible get it merged soon? Would really like to have this before next release.