docs: multiple minor docstring fixes

[alexander-held]

This adopts np.ndarray in docstrings, where in some cases previously numpy.ndarray was used. The type of cabinetry.fit.results_containers.LimitResults.observed_limit was wrong in the docstring, this is also fixed. A few issues flagged by pydocstyle (via pydocstyle --convention google src/cabinetry/) are also fixed, and pre-commit is updated.

* harmonized use of np.ndarray in docstrings
* fixed type of LimitResults.observed_limit in docstring
* multiple minor docstring formatting fixes
* pre-commit updated

[codecov]

Codecov Report

Merging #274 (3f823b9) into master (894ed2a) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #274   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           19        19           
  Lines         1798      1798           
  Branches       279       279           
=========================================
  Hits          1798      1798           

Impacted Files	Coverage Δ
src/cabinetry/contrib/histogram_creation.py	100.00% <ø> (ø)
src/cabinetry/fit/results_containers.py	100.00% <ø> (ø)
src/cabinetry/histo.py	100.00% <ø> (ø)
src/cabinetry/model_utils.py	100.00% <ø> (ø)
src/cabinetry/template_builder.py	100.00% <ø> (ø)
src/cabinetry/visualize/plot_model.py	100.00% <ø> (ø)
src/cabinetry/workspace.py	100.00% <ø> (ø)

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