fix: Add TYPE_CHECKING guard for numpy.typing

[matthewfeickert]

Description

Resolves #2207

The addition of typing.TYPE_CHECKING avoids situations in which the version of NumPy (whose lower bounds is enforced by SciPy) doesn't have numpy.typing, which was added in NumPy v1.21.0.

To avoid drops in code coverage at the patch level, exclude if TYPE_CHECKING: from the coverage report by using the exclude_also option.

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

* The addition of typing.TYPE_CHECKING avoids situations in which
  the version of NumPy (whose lower bounds is enforced by SciPy)
  doesn't have numpy.typing, which was added in NumPy v1.21.0.
* Exclude lines that match 'if TYPE_CHECKING:' from the coverage
  report to avoid artificial drops in code coverage.
   - c.f. https://coverage.readthedocs.io/en/stable/excluding.html#advanced-exclusion

Co-authored-by: Giordon Stark <kratsg@gmail.com>

[matthewfeickert]

Example of things working:

$ docker run --rm -ti python:3.8 /bin/bash
root@34efcf32f365:/# python -m venv venv && . venv/bin/activate
(venv) root@34efcf32f365:/# python -m pip --quiet install --upgrade pip setuptools wheel
(venv) root@34efcf32f365:/# python -m pip --quiet install --upgrade 'numpy==1.17.3' 'scipy==1.5.1'
venv) root@34efcf32f365:/# git clone --branch fix/guard-numpy-typing --single-branch https://github.com/scikit-hep/pyhf
Cloning into 'pyhf'...
...
(venv) root@34efcf32f365:/# cd pyhf
(venv) root@34efcf32f365:/pyhf# python -m pip --quiet install --upgrade .
(venv) root@34efcf32f365:/pyhf# cd
(venv) root@34efcf32f365:~# python -m pip list | grep 'numpy\|scipy'
numpy                1.17.3
scipy                1.5.1
(venv) root@34efcf32f365:~# python -c 'import pyhf'
(venv) root@34efcf32f365:~# echo $?
0

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (22c1699) 98.30% compared to head (771f64d) 98.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2208   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files          69       69           
  Lines        4533     4533           
  Branches      801      801           
=======================================
  Hits         4456     4456           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	97.88% <100.00%> (ø)
doctest	61.12% <100.00%> (ø)
unittests-3.10	96.31% <100.00%> (ø)
unittests-3.11	96.31% <100.00%> (ø)
unittests-3.8	96.33% <100.00%> (ø)
unittests-3.9	96.36% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pyhf/tensor/numpy_backend.py	98.61% <100.00%> (ø)

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