Move scipy to optional requirements

[rly]

See #1140

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.88%. Comparing base (ff4a0aa) to head (2f17516).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1233   +/-   ##
=======================================
  Coverage   90.87%   90.88%           
=======================================
  Files          42       42           
  Lines        9524     9532    +8     
  Branches     1921     1922    +1     
=======================================
+ Hits         8655     8663    +8     
  Misses        576      576           
  Partials      293      293           

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[mavaylon1]

@rly Before I approve, could you add tests or coverage skips for the missing lines.

[rly]

@rly Before I approve, could you add tests or coverage skips for the missing lines.

Thanks. Good catch. After merging the changes in pyproject.toml, scipy crept back in as a primary dependency, and so no coverage tests were run without scipy installed.