perf(parquet): batch delta binary packed decoding

[fallintoplace]

Rationale for this change

DELTA_BINARY_PACKED decoding called BitReader.GetBatch once for every value in a miniblock. The miniblock is already the unit decoded by this code, so this missed the existing batch unpackers.

What changes are included in this PR?

• decode each miniblock into reusable scratch with one GetBatch call
• keep 33 to 64 bit values on the generic uint64 path instead of the 32 bit SIMD unpackers
• read SIMD input directly into pooled scratch so batched calls do not add allocations
• add int32 and int64 benchmarks with nonzero packed widths
• add coverage for batched values from 33 through 64 bits

Are these changes tested?

Yes. I ran the full Parquet test tree with the parquet-testing fixtures, the internal utility and encoding tests with noasm, and a linux/amd64 cross-build.

Apple M1 Pro results for 65,536 values with GOMAXPROCS=1 and 10 samples:

Workload	Time
int32 small deltas	-58.86%
int32 alternating wide deltas	-66.04%
int64 timestamp-like deltas	-59.72%
int64 deltas wider than 32 bits	-33.89%

Allocations stay at 2 allocs/op in all four benchmarks.