Function preload_parquet_meta_cache_for_files 

async fn preload_parquet_meta_cache_for_files(
    region_id: RegionId,
    cache_manager: CacheManagerRef,
    sst_meta_cache_capacity: u64,
    table_dir: String,
    path_type: PathType,
    object_store: ObjectStore,
    files: Vec<FileHandle>,
) -> usize

Preloads Parquet metadata into the in-memory SST meta cache on region open.

This improves the latency of the first query after server start by avoiding large Parquet metadata reads on demand.

The preload is best-effort:

• Always tries to warm from the local write cache (file cache) first.
• If the region storage backend is local filesystem (Scheme::Fs), it may also load metadata directly from the local store.
• It will not fetch metadata from remote object stores (S3/GCS/OSS/…).