feat: Improve warnings for qmu and qmu_tilde for the set POI bounds

[lorenzennio]

Description

When running

model = pyhf.simplemodels.uncorrelated_background(signal=[5.0, 10.0], bkg=[50.0, 60.0], bkg_uncertainty=[5.0, 12.0])
pyhf.infer.hypotest(1.0, [53.0, 65.0] + model.config.auxdata, model, test_stat="qmu")

we get a warning

qmu test statistic used for fit configuration with POI bounded at zero.
Use the qmu_tilde test statistic (pyhf.infer.test_statistics.qmu_tilde) instead.

and vice versa for POIs not bounded at 0.

But this should also tell you to set test_stat="qtilde" or (test_stat="q").

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Add information to the user in the warning that provides them with the
  higher level pyhf.infer APIs kwarg to set the correct test statistic.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4d215a7) 96.29% compared to head (efe4ba2) 98.28%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2390      +/-   ##
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+ Coverage   96.29%   98.28%   +1.98%     
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  Files          69       69              
  Lines        4539     4539              
  Branches      648      803     +155     
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+ Hits         4371     4461      +90     
+ Misses        128       45      -83     
+ Partials       40       33       -7     

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contrib	97.86% <ø> (?)
doctest	60.71% <ø> (?)
unittests-3.10	96.29% <ø> (ø)
unittests-3.11	96.29% <ø> (?)
unittests-3.8	96.32% <ø> (?)
unittests-3.9	96.34% <ø> (?)

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[matthewfeickert]

Thanks @lorenzennio. So this is good, but these log warnings are raised in the test stat APIs themselves, where there is no test_stat kwarg, as the API is already the test stat. So I would suggest on a newline (as this will get long otherwsise) noting that if the user is calling from the pyhf.infer.mle APIs or pyhf.infer.hypotest this can be set via kwarg.

[matthewfeickert]

@lorenzennio This fix is now out in pyhf v0.7.6.