Function _parquet_metadata_pruned_json 

pub fn _parquet_metadata_pruned_json(
    path: &str,
    projection: Vec<String>,
    predicate: Vec<String>,
) -> PyResult<String>

Decode a parquet footer, apply FileMetadata::pruned(projection, predicate), and return the result as a JSON string. Format-agnostic custom serde lets the same wire DTOs emit JSON for inspection or bincode for dispatch.

Used by py-polars tests to assert structural prune behavior (only kept columns survive, stats only on predicate columns). Local files only.