Turn velocity plot test into a figure test

[svank]

PR summary

It's a figure test now

[svank]

Note that pytest needs to have '--mpl' added to the command line to actually run the comparison. I like to make that happen by default like this

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.15%. Comparing base (f0cfdc1) to head (6d6e246).
Report is 40 commits behind head on main.

Files with missing lines	Patch %	Lines
punchbowl/level3/velocity.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #325      +/-   ##
==========================================
- Coverage   86.97%   86.15%   -0.83%     
==========================================
  Files          56       56              
  Lines        3717     3793      +76     
==========================================
+ Hits         3233     3268      +35     
- Misses        484      525      +41     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jmbhughes]

@svank can you look at the CI for this? Thanks!

[svank]

Looks like this repo doesn't use pytest-arraydiff, so the --arraydiff flag was being rejected. Let's try this.