GH-3522: Add batch read APIs to ValuesReader hierarchy

[iemejia]

Summary

• Add readIntegers(), readLongs(), readFloats(), readDoubles() batch methods to ValuesReader with default loop-based implementations
• Override in specialized readers to amortize per-value overhead across batches

Overrides

• RunLengthBitPackingHybridDecoder.readInts(): batch across RLE runs and packed groups using Arrays.fill/System.arraycopy
• DictionaryValuesReader: batch-decode dictionary IDs first, then batch-lookup values (eliminates per-value IOException try/catch)
• DeltaBinaryPackingValuesReader: System.arraycopy from pre-decoded buffer
• PlainValuesReader (all types): loop over LittleEndianDataInputStream
• ByteStreamSplitValuesReader (all types): indexed ByteBuffer bulk read

Rationale

These APIs enable callers to amortize per-value overhead (virtual dispatch, bounds checks, mode switches) across batches. Combined with other optimizations in this series (ByteBuffer-based RLE decoder, etc.), batch reads yield significant throughput improvements over per-value loops.

All 576 parquet-column tests pass.

[iemejia]

Closing — the batch read APIs will be superseded by forthcoming PRs for column I/O (v2-par7-column-io) and level write batching (v2-par9-level-write-batching), which are not yet opened because they depend on #3565 (PLAIN), #3568 (RLE), and other encoding PRs being merged first.

I initially submitted a series of small, focused PRs thinking they'd be easier to review. In practice the sheer number (~16 PRs, with more pending) made things harder to follow — even for me. I've regrouped the changes by encoding type / performance area so that each PR is self-contained with its own benchmarks and test coverage, which should make review and performance analysis much more straightforward.

Apologies for the churn. The replacement PRs will be opened once their dependencies land. Thank you.