feat: Support ShapeFactor for import/export

[kratsg]

Description

Resolves #1080. This adds in the shapefactor import. ./cc @alexander-held

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• 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

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* Add ShapeFactor support to pyhf.readxml
* Add ShapeFactor support to pyhf.writexml
* Add ShapeFactor test

[lukasheinrich]

we should add a validatiion test based on a xml config.
e.g. ./xmlimport_input/config/examples/example_DataDriven_controlRegion.xml

[kratsg]

we should add a validatiion test based on a xml config.
e.g. ./xmlimport_input/config/examples/example_DataDriven_controlRegion.xml

I did: https://github.com/scikit-hep/pyhf/pull/1136/files#diff-2888ad0d96a0c85176d2918eb8a5d09dbebe4ea4724bb2497f5b4b9f70dc0536R328-R332

[lukasheinrich]

ah missed that!

[codecov]

Codecov Report

Merging #1136 into master will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1136      +/-   ##
==========================================
+ Coverage   97.02%   97.14%   +0.11%     
==========================================
  Files          62       62              
  Lines        3598     3603       +5     
  Branches      519      521       +2     
==========================================
+ Hits         3491     3500       +9     
+ Misses         66       64       -2     
+ Partials       41       39       -2     

Flag	Coverage Δ
#unittests	97.14% <100.00%> (+0.11%)	⬆️

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Impacted Files	Coverage Δ
src/pyhf/readxml.py	94.30% <100.00%> (+1.35%)	⬆️
src/pyhf/writexml.py	95.74% <100.00%> (+1.54%)	⬆️

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[matthewfeickert]

Thanks for this @kratsg. LGTM.