docs: Add typehint aliases

[kratsg]

Pull Request Description

Resolves #1964.

Link to docs render: https://pyhf--1969.org.readthedocs.build/en/1969/_generated/pyhf.tensor.numpy_backend.numpy_backend.html#pyhf.tensor.numpy_backend.numpy_backend

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

* Use Sphinx autodoc typehint aliases to improve readability of documentation.
   - c.f. https://www.sphinx-doc.org/en/master/usage/extensions/autodoc.html#confval-autodoc_type_aliases

[codecov]

Codecov Report

Merging #1969 (222d3ab) into master (62aad71) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1969      +/-   ##
==========================================
- Coverage   98.24%   98.10%   -0.14%     
==========================================
  Files          68       68              
  Lines        4377     4378       +1     
  Branches      726      726              
==========================================
- Hits         4300     4295       -5     
- Misses         45       48       +3     
- Partials       32       35       +3     

Flag	Coverage Δ
contrib	26.58% <100.00%> (+0.01%)	⬆️
doctest	60.57% <100.00%> (+<0.01%)	⬆️
unittests-3.10	96.13% <100.00%> (+<0.01%)	⬆️
unittests-3.7	?
unittests-3.8	?
unittests-3.9	?

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	98.59% <100.00%> (+<0.01%)	⬆️
src/pyhf/schema/variables.py	75.00% <0.00%> (-25.00%)	⬇️
src/pyhf/schema/loader.py	90.90% <0.00%> (-9.10%)	⬇️
src/pyhf/utils.py	91.83% <0.00%> (-4.09%)	⬇️

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[matthewfeickert]

LGTM. 👍 Thanks @kratsg!