fixup! refactor: extract MeanMaterialBudget to standalone function

Author: olantwin

CHANGELOG.md

@@ -208,6 +208,7 @@ it in future.
   - Update Python code in shipDigiReco.py to use modern constructors
   - Bump ClassDef versions to 2 for schema evolution
   - Add TrackInfo to RNTuple I/O test suite
+  - Move MeanMaterialBudget to standalone function to reduce duplication and allow proper attribution of code to ALICE
 
 ### Removed