Add pre-commit caching to CI

[bachya]

Describe what the PR does:

This PR adds caching to pre-commit hooks, which should make CI run faster.

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Update README.md with any new documentation.
• Add yourself to AUTHORS.md.

[codecov]

Codecov Report

Merging #27 into dev will not change coverage by %.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               dev       #27   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          142       142           
=========================================
  Hits           142       142           

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[codeclimate]

Code Climate has analyzed commit 2b3879c and detected 0 issues on this pull request.

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