[WIP] Parquet Java ALP Implementation

[vinooganesh]

cc @julienledem @alamb

Rationale for this change

Reworks the ALP encoding implementation to address emkornfield's architectural feedback on PR #3390. The original buffered all values in memory and decoded eagerly. This makes the writer incremental (encode per-vector as values arrive) and the reader lazy (decode on demand), matching how other Parquet encodings work.

Builds on Julien Le Dem's original implementation (#3390). File structure, integration points, core math, and interop test infrastructure all come from his work. The rework focused on the internal writer/reader plumbing.

What changes are included in this PR?

Architecture (addressing review feedback):

• Incremental writer. Values buffer in a fixed-size vector, each full vector encodes and flushes immediately.
• Lazy reader. Vectors decode on first access via offset array, skip() is O(1).
• Interleaved page layout so each vector is self-contained.
• Extracted AlpValuesReader abstract base class for shared logic.
• Preset caching. Full parameter search for first 8 vectors, top 5 combos cached for the rest.

Spec compliance:

• Fixed packed data size formula to ceil(n * bitWidth / 8)
• Fixed unsigned delta comparison in float writer
• Explicit little-endian byte reads instead of relying on ByteBuffer order
• Using parquet-encoding's BytePacker instead of custom bit-packing
• Capped max vector size at 32768 to prevent uint16 overflow in num_exceptions

Code quality:

• Renamed bitWidth overloads to prevent silent type coercion
• Package-private visibility for internals
• Configurable vector size (default 1024)

Integration:

• Wired ALP into DefaultV2ValuesWriterFactory and ParquetProperties

Are these changes tested?

Yes. 105 tests across 3 test classes, all passing. Full parquet-column suite (677 tests) also passes.

Key tests construct ALP page bytes directly according to the spec and feed them to the reader without going through the writer. This verifies the reader works independently and catches any bugs where writer and reader agree with each other but disagree with the spec. Also covers NaN bit pattern preservation, negative zero roundtrip, extreme values, every partial vector remainder mod 8, skip across vector boundaries, and preset caching under distribution change.

Are there any user-facing changes?

Users can enable ALP encoding for FLOAT and DOUBLE columns via ParquetProperties.withAlpEncoding(), globally or per-column.

Note: Likely me missing something - but ALP is not yet in the parquet-format Thrift spec (apache/parquet-format#533), so writing ALP files through the full Hadoop pipeline will fail at metadata serialization until parquet.thrift is updated (parquet-format PR #548).

[prtkgaur]

The code organization looks good to me and the code follows the spec. I looked for areas of any extra buffer allocations which might impact performance and I think it is optimally written.

I think we should add a few benchmarks and publish numbers from them.

Thanks for working on this Vinoo!

[prtkgaur]

Wanted to make sure we have the following testing.

For the cross compatibility testing are we making sure that we write both V1 and V2 pages and the implementation in other language is able to read it.