add support for using @showprogress on Threads.@threads for loops

[Fro116]

This lets you use the @showprogress macro on parallel for loops. For example,

@showprogress Threads.@threads for i in 1:100
    sleep(0.1)
end

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5b3bd1d) 96.81% compared to head (0ca12d5) 97.03%.
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
+ Coverage   96.81%   97.03%   +0.22%     
==========================================
  Files           1        1              
  Lines         533      539       +6     
==========================================
+ Hits          516      523       +7     
+ Misses         17       16       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Fro116]

My bad, I never tested on older versions of Julia. The Threads.@threads had a different expression tree before v1.3.0-rc1 and so the new test I added was failing on older builds.

I'll gate the Threads.@threads test behind a @static if VERSION >= v"1.3.0-rc1" statement, the same way we do for some Threads.@Spawn tests in test_threads.jl.

[Fro116]

Take three. I updated to fix the code coverage errors.

The last run failed on the nightly ubuntu-latest build because the test case "test_threads.jl ProgressUnknown" errored out. I'm not sure why. That test should not touch any of the code in this pr. I can't repro it, and it didn't fail in the first run (https://github.com/timholy/ProgressMeter.jl/actions/runs/6859117251/job/18660114093?pr=284). Is the test flaky on master?

[MarcMush]

Recently yes
Ref #281

[Fro116]

Okay, afaict this passes everything except for the flaky test. Should be good to go, but let me know if there's anything else I should look into.

[MarcMush]

support for @Threads.threads is very welcome!

[MarcMush]

LGTM