Fix chunkedgraph edit combine and add caching

[jefferis]

Summary

• fix operation detail data-frame assembly when chunked responses include empty batches or missing names
• add incremental on-disk caching for chunkedgraph operation fetches using Arrow plus a missing-op sidecar cache
• add regression tests for the combine path and cache append/schema-drift behavior

Testing

• Rscript -e "for (f in list.files('R', full.names=TRUE)) parse(file=f); cat('Parsed', length(list.files('R', full.names=TRUE)), 'R files successfully\n')"