fix(instrumentation-runtime-node): use TestMetricReader, unref timer

[pichlermarc]

Which problem is this PR solving?

• tests were failing as the utilization ended up being 1 (fix(instr-perf-hooks): avoid 'prepare' npm script because that runs on 'npm install' #1955) . This might have happened as the collection happened at a time where event loop was fully utilized. This PR attempts to fix this by doing two things:
  • changing the PeriodicExportingMetricReader to avoid having to wait for collection, getting rid of one variable that might break tests
  • allowing <=1 as a value as it's a valid value for a fully utilized event loop (which can happen in some cases as collection does not need to wait for anything that's not doing work on the event loop).
• for me the process kept running as disable() was never called when the test failed. I can see this happening in apps too as it's rather uncommon to disable() instrumentations before shutting down. Therefore in unrefed the timer when it's created.

Fixes #1960

[codecov]

Codecov Report

Merging #1965 (bc77574) into main (ff40cc8) will decrease coverage by 0.06%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head bc77574 differs from pull request most recent head 07855ba. Consider uploading reports for the commit 07855ba to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1965      +/-   ##
==========================================
- Coverage   91.03%   90.97%   -0.06%     
==========================================
  Files         146      146              
  Lines        7492     7492              
  Branches     1501     1502       +1     
==========================================
- Hits         6820     6816       -4     
- Misses        672      676       +4     

Files	Coverage Δ
...nstrumentation-runtime-node/src/instrumentation.ts	89.18% <100.00%> (-10.82%)	⬇️

[d4nyll]

replacing interval-based collection with on-demand collection

@pichlermarc thanks for cleaning up these tests, they look much sturdier now

unref

Good call 👍

[trentm]

TIL: the arrange-act-assert pattern name (http://wiki.c2.com/?ArrangeActAssert)