fix: add threshold to codecov project check for expanded coverage scope

Expanding coverage from anoph/ only to the full malariagen_data/ package
causes an expected drop in the project coverage percentage because newly
measured modules (plasmodium.py, veff.py, util.py, etc.) have lower test
coverage. This adds a 10% threshold to the project status check so that
the expected one-time drop from the scope expansion does not block the PR.

The patch check remains strict (80% target, 0% threshold) to ensure all
new/modified code is well tested.

Author: kunal-10-cloud

.codecov.yml

@@ -3,6 +3,7 @@ coverage:
     project:
       default:
         target: auto
+        threshold: 10%
     patch:
       default:
         target: 80%