Draw observation radii on field standard-deviation plots

[dafeda]

Screen.Recording.2026-05-27.at.14.05.41.mov

Running heat equation:

(ert) ➜  eb76609f-986d-4a6b-bced-98519cbe4094 git:(plot-obs-radius) ✗ tree -L 2
.
├── index.json
├── localization
│   ├── COND.metadata.npz
│   └── COND.npz
├── observations
│   └── summary
├── templates
└── templates.json

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.81250% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.53%. Comparing base (9def804) to head (cc65c30).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ert/gui/tools/plot/plottery/plots/std_dev.py	81.03%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13622      +/-   ##
==========================================
- Coverage   89.54%   89.53%   -0.02%     
==========================================
  Files         464      464              
  Lines       32776    32841      +65     
==========================================
+ Hits        29349    29403      +54     
- Misses       3427     3438      +11     

Flag	Coverage Δ
cli-tests	35.69% <0.00%> (-0.07%)	⬇️
fuzz	43.89% <17.18%> (+0.07%)	⬆️
gui-tests	59.74% <20.31%> (-0.08%)	⬇️
performance-and-unit-tests	78.09% <82.81%> (+<0.01%)	⬆️
test	45.35% <17.18%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/ert/field_utils/field_utils.py	93.71% <100.00%> (+0.15%)	⬆️
src/ert/gui/tools/plot/plottery/plots/std_dev.py	89.47% <81.03%> (-6.58%)	⬇️

... and 4 files with indirect coverage changes