fix: Make p-value-like values 0-d tensors

[matthewfeickert]

Description

Resolves #1268

Ensure all p-value-like values and test statistics are given as 0-d tensors and harmonize returns types across calculator types.

ReadTheDocs build: https://pyhf.readthedocs.io/en/fix-ensure-p-value-like-return-type/

• pyhf.infer.calculators.AsymptoticCalculator
• pyhf.infer.calculators.ToyCalculator

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

* Ensure p-value-like values and test statistics are all 0-d tensors for consistent return type
   - Update docstrings
* Harmonize return types from asymptotic and toy calculators

[codecov]

Codecov Report

Merging #1311 (79e7a34) into master (ae9e39c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1311   +/-   ##
=======================================
  Coverage   97.49%   97.50%           
=======================================
  Files          63       63           
  Lines        3758     3760    +2     
  Branches      537      538    +1     
=======================================
+ Hits         3664     3666    +2     
  Misses         55       55           
  Partials       39       39           

Flag	Coverage Δ
unittests	97.50% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/pyhf/infer/utils.py	100.00% <ø> (ø)
src/pyhf/infer/calculators.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ae9e39c...79e7a34. Read the comment docs.

[matthewfeickert]

cc @alexander-held for feedback on any downstream problems with this.

[alexander-held]

cc @alexander-held for feedback on any downstream problems with this.

Thanks! cabinetry currently does not use infer.calculators directly, so this has no direct impact and all tests run fine.