print commit hash on import; fix event_id offset in multi-core steps

G4Calo.py prints the commit at import time, resolved via a
minicalo_version.py file (baked in by Docker) or git rev-parse
from the file's directory as fallback.

event_id in the Steps ntuple restarts from 0 in each subprocess;
_assemble_results_to_mini_df now accepts per-file event_id_offsets
so IDs are globally unique after merging. run_batch passes cumulative
nevents as offsets when loading the Steps tree.

Dockerfiles write minicalo_version.py before copying Python files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile-cpu

@@ -99,7 +99,8 @@ ADD minicalosim /root/minicalosim
 RUN cd  /root/minicalosim && git checkout $COMMIT && \
     git submodule update --init lib/pybind11 && \
     mkdir -p build && cd build && rm -rf * && cmake ../ && make -j$(nproc) &&\
-    cp minicalo* ../bind/G4Calo.py /usr/local/lib/python3.8/dist-packages/
+    echo "commit = '${COMMIT}'" > ../bind/minicalo_version.py && \
+    cp minicalo* ../bind/G4Calo.py ../bind/minicalo_version.py /usr/local/lib/python3.8/dist-packages/