Summary

• Adds conservative scan-time metadata pruning for metrics splits after the metastore split list is fetched.
• Extracts string equality and IN predicates from DataFusion filters and evaluates them against split metadata before building Parquet file groups.
• Prunes with exact metric_name metadata, exact low-cardinality tag metadata, and per-column zonemap_regexes when present.
• Keeps splits when relevant metadata is missing or a zonemap regex is invalid, so older or partially populated metadata cannot produce false negatives.
• Marks metric and tag predicates as inexact pushdown so DataFusion passes them into the TableProvider scan while still applying the row-level filter later.
• Updates the metrics integration test helper to preserve writer-produced zonemap metadata and adds an end-to-end pruning regression test.

Notes

This intentionally does not push tag predicates into the metastore query yet. Metric name and time range still drive metastore-side pruning; tag and zonemap pruning runs locally on returned split metadata before Parquet files are read.

Testing

• cargo fmt --package quickwit-datafusion
• cargo test -p quickwit-datafusion