feat(instrumentation-fs): require parent span

[unflxw]

Which problem is this PR solving?

• The fs instrumentation, unlike other instrumentations, does not have a requireParentSpan option, in order to only trace calls to the fs module that happen in the context of a broader action. Applications might, for example, read some files during boot, which would rarely make for useful traces.

Short description of the changes

• Add a requireParentSpan option, which defaults to false. If set to true, calls to the fs module will not be instrumented unless the current active context has a span, so the fs instrumentation will never create a trace of its own.

[codecov]

Codecov Report

Merging #1335 (6c8e038) into main (04d583b) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1335   +/-   ##
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  Coverage   96.08%   96.08%           
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  Files          14       14           
  Lines         893      893           
  Branches      191      191           
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  Hits          858      858           
  Misses         35       35           

[blumamir]

Thanks for working on this
I added a few comments about code style. They are all non-blocker and optional, so feel free to resolve them if you think otherwise.

[unflxw]

Thank you for the comments @blumamir! They make a lot of sense to me -- the naming around the test generator function is very wonky. I'll address these the coming week.

[unflxw]

Done. Feel free to merge if the tests pass 🚀

EDIT: not sure why the tests don't pass -- the linter seems to be unhappy about a file that isn't changed by this PR?