feat: task-level input metrics (bytesRead) for Iceberg native scan

[mbutrovich]

Which issue does this PR close?

Closes #4002.

Rationale for this change

Iceberg native scans report zero for task-level input metrics (bytesRead, recordsRead) in Spark UI because iceberg-rust reads files entirely in Rust, bypassing Hadoop's Java I/O counters. Upstream iceberg-rust PR apache/iceberg-rust#2349 added ScanMetrics with a live bytes_read counter. This PR plumbs that through to Spark.

What changes are included in this PR?

• Bump iceberg-rust dep from a2f067d to 1ad4bfd (adds ScanResult/ScanMetrics)
• ArrowReader::read() now returns ScanResult: extract stream and clone metrics handle
• Add bytes_scanned Count metric to IcebergScanMetrics, bridge iceberg-rust's live AtomicU64 into the DF metric tree on each poll_next via delta tracking
• Add bytes_scanned SQLMetric to CometIcebergNativeScanExec
• Override CometExecRDD.compute() to call reportScanInputMetrics (same pattern as the Parquet path)
• Remove stale configured_scheme field from OpenDalStorageFactory::S3 (upstream API change)

How are these changes tested?

• Added bytes_scanned > 0 assertion to existing "verify all Iceberg planning metrics" test
• New test: "task-level inputMetrics.bytesRead is populated for Iceberg native scan" — uses SparkListener to verify bytesRead > 0, recordsRead == 10000, and cross-checks SQL-level bytes_scanned matches task-level bytesRead

[mbutrovich]

Thanks for the feedback @andygrove, @comphead, and @hsiang-c! Hopefully I addressed all comments and clarified in the user guide for Iceberg.

[comphead]

Thanks @mbutrovich

[hsiang-c]

LGTM, thanks @mbutrovich