Add cohort_geometries() to access cohort GeoJSON metadata

[adilraza99]

Summary

Add a new cohort_geometries() method to expose cohort boundary geometries through the API.

Changes

• add cohort_geometries() to AnophelesSampleMetadata
• load GeoJSON cohort boundary data using the standard json library
• add caching consistent with existing metadata access patterns
• validate accepted cohort_set values
• add tests and minimal GeoJSON fixtures

Impact

Provides access to cohort geometry metadata while keeping the API simple and dependency-free.

Part of #435

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.27%. Comparing base (ab59c87) to head (0606d4b).
⚠️ Report is 43 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1053      +/-   ##
==========================================
+ Coverage   90.25%   90.27%   +0.02%     
==========================================
  Files          51       51              
  Lines        5631     5678      +47     
==========================================
+ Hits         5082     5126      +44     
- Misses        549      552       +3     

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[adilraza99]

Hi @jonbrenas, CI checks are passing now.
Could you please take a look when you have a moment?

[jonbrenas]

Hi @adilraza99, could you create a notebook with an example of how to use this new function?

[adilraza99]

Thanks for taking a look! Sure, I can add a small example notebook showing how to use the cohort_geometries() function. I'll add it shortly.

[adilraza99]

@jonbrenas
Thanks! I've added an example notebook demonstrating how to use the cohort_geometries() API, and verified that it runs correctly.

Also noting that the work for this issue is split across two PRs - this one and the earlier PR that addressed the first part of #435.