Move heatmap functionality to brainglobe-utils

[adamltyson]

Moves the heatmap generation functionality to brainglobe-utils

Part of #73

Depends on brainglobe/brainglobe-utils#22, and tests will fail until that's merged and released.

[willGraham01]

Approving, pending CI checks once https://github.com/brainglobe/brainglobe-utils/actions/runs/7445454585 completes and releases

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (2da996a) 81.39% compared to head (b0a36bf) 82.24%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
...rainglobe_workflows/brainmapper/analyse/analyse.py	7.14%	13 Missing ⚠️
brainglobe_workflows/brainmapper/main.py	37.50%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
+ Coverage   81.39%   82.24%   +0.84%     
==========================================
  Files          32       27       -5     
  Lines        1586     1538      -48     
==========================================
- Hits         1291     1265      -26     
+ Misses        295      273      -22     

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