Calculate spot/pixel distances from the stimulus

[tmcgrath325]

Adds spot_distances() and pixel_distances(), which calculate the distance in pixels from the centroid of the stimulus for all segmented spots or pixels, respectively.

[codecov]

Codecov Report

❌ Patch coverage is 8.00000% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.55%. Comparing base (b9cc3b0) to head (c48ce6f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/distances.jl	0.00%	15 Missing ⚠️
src/segment.jl	20.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
- Coverage   98.29%   90.55%   -7.74%     
==========================================
  Files           4        5       +1     
  Lines         293      307      +14     
==========================================
- Hits          288      278      -10     
- Misses          5       29      +24     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.