Add native prepared Parquet batches

[platypii]

Summary

• expose Iceberg field-id schemas and Squirreling 0.16 prepareScan() sources
• yield one native batch per Parquet row group with independently deferred, selection-aware columns
• preserve decoded arrays as native vectors, use offset indexes for narrowed ranges, and reuse decoded covering ranges when a field participates in both filtering and output
• retain scan() and scanColumn() compatibility; snapshots with delete files use the existing delete-aware row scanner through the bounded row-to-batch adapter

End-to-end benchmarks

Measured on Node v26.5.1 with squirreling@0.16.1 against two current local Hypaware Iceberg tables containing 339,953 rows. The seven-query suite is derived from Hypaware overview, retrieval, and top-K workloads and filters to the most recent seven days. Before timing each query, the released baseline, same-engine legacy source, and prepared source were exact-compared. Medians are from three alternating runs with explicit garbage collection.

The prepared source is 1.31× faster geometrically than the same Squirreling 0.16.1 engine using Icebird's legacy row source, with every query faster. It is 1.35× faster geometrically than the released Icebird 0.8.22 / Squirreling 0.15.3 pair.

Query	Legacy source	Prepared source	Source speedup	Legacy peak heap	Prepared peak heap
Overview date counts	203.34 ms	139.09 ms	1.46×	57.22 MiB	43.37 MiB
Tool calls and sessions	95.82 ms	86.66 ms	1.11×	49.84 MiB	49.50 MiB
Provider/model JSON tokens	804.94 ms	411.57 ms	1.96×	244.98 MiB	65.71 MiB
Daily sessions and JSON tokens	590.32 ms	389.92 ms	1.51×	238.96 MiB	65.38 MiB
Selective tool-result payload	7.38 ms	6.27 ms	1.18×	9.69 MiB	7.45 MiB
Recent attributes preview	6.55 ms	6.30 ms	1.04×	10.57 MiB	8.64 MiB
Largest recent system prompts	385.34 ms	346.80 ms	1.11×	228.85 MiB	172.47 MiB

The provider/model rollup requested the same 77.49 MiB through both source implementations, attributing its 1.96× improvement to native batching rather than reduced I/O. Peak heap measurements are sampled every 5 ms and are directional.

Validation

• npm test — 59 files, 686 tests passed
• npm run lint
• npx tsc
• npm run build:types — no tracked declaration diff

This depends only on the already-published squirreling@0.16.1 release.