Add ArrayPlugin to enable serde for new DecimalBytePartsArray format

[mhk197]

Summary

Add serialization for DecimalBytePartsArray with lower parts while preserving the frozen v1 file format. DecimalBytePartsPlugin owns both formats and selects the serialized ID from the array's layout:

Array layout	Serialized ID
Signed most significant part (MSP) only	vortex.decimal_byte_parts
Signed MSP plus one to three unsigned lower parts	vortex.decimal_byte_parts_v2

Both formats deserialize into the same in-memory array representation. Each lower part represents a 64-bit window, but its storage dtype may be narrowed to u8, u16, or u32 when its values fit.

Changes

• Record the MSP's physical integer type, lower-part count, and each lower part's physical integer type in metadata. Deserialization validates these types and restores each child with its recorded dtype.
• Keep the frozen format restricted to zero lower parts and require at least one for v2. Frozen metadata remains byte-identical.
• Make DBP's VTable serialize and deserialize methods return errors directing callers to DecimalBytePartsPlugin. Keep DBP metadata and serde helpers in plugin.rs so the dedicated plugin owns both formats.
• Add a separate v2 compatibility fixture covering positive and negative wide i128 values and nullable i256 values. The frozen fixture is unchanged.

API Changes

Breaking: directly registering DecimalByteParts, or calling its VTable serde methods, now errors for both serialization and deserialization, including the frozen v1 format. Replace:

session.arrays().register(DecimalByteParts);

with:

session.arrays().register(DecimalBytePartsPlugin);

vortex_decimal_byte_parts::initialize(&session) already registers the plugin. Existing v1 files remain readable through it; no file migration is required.

[codspeed]

Merging this PR will degrade performance by 19.87%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 12 improved benchmarks
❌ 18 regressed benchmarks
✅ 2205 untouched benchmarks
⏩ 229 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	column_x_constant[2]	131.3 µs	454.3 µs	-71.09%
❌	Simulation	column_x_constant[32]	132 µs	390.1 µs	-66.16%
❌	Simulation	column_x_column[2]	101.8 µs	203.1 µs	-49.85%
❌	Simulation	column_x_constant[256]	311.9 µs	590.3 µs	-47.17%
❌	Simulation	nullable[2]	324.1 µs	591 µs	-45.17%
❌	Simulation	non_nullable[2]	327.9 µs	593.2 µs	-44.73%
❌	Simulation	column_x_extension_constant[2]	147.1 µs	246.9 µs	-40.41%
❌	Simulation	nullable[2]	416.8 µs	629.4 µs	-33.78%
❌	Simulation	non_nullable[2]	418.9 µs	630.4 µs	-33.55%
❌	Simulation	column_x_extension_constant[256]	277.8 µs	415.2 µs	-33.09%
❌	Simulation	random_i8[0.8]	72.9 µs	98.1 µs	-25.76%
❌	Simulation	column_x_extension_constant[32]	135.2 µs	167.7 µs	-19.39%
❌	Simulation	column_x_column[32]	76.8 µs	94.1 µs	-18.38%
❌	Simulation	decompress[datetime_for_bp]	159.3 µs	193.6 µs	-17.68%
❌	WallTime	arrow_checked_add_u32_avx2[16384]	17.6 µs	21.3 µs	-17.21%
❌	Simulation	column_x_column[256]	75.2 µs	88.5 µs	-15.04%
❌	Simulation	optimize_lookup_predicate[ids=16, shape=balanced_or]	70 µs	80.9 µs	-13.45%
❌	WallTime	dbp_split_kernel_mixed_null_neon[(I256, 1024)]	1.9 µs	2.2 µs	-12.44%
⚡	Simulation	random_i16[0.95]	98.5 µs	76 µs	+29.6%
⚡	Simulation	random_i8[0.01]	45.3 µs	39.7 µs	+14.22%
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing mk/dbp-serde (8ba61cc) with mk/dbp-v2-feature (8fc58e0)}

Footnotes

1. 229 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[joseph-isaacs]

I thought the new array in mem would have v2? So we would have v1 == "" here

Suggested change

	pub fn decimal_byte_parts_v2_id() -> ArrayId {
	static ID: CachedId = CachedId::new("vortex.decimal_byte_parts_v2");
	*ID
	pub fn decimal_byte_parts_v2_id() -> ArrayId {
	static ID: CachedId = CachedId::new("vortex.decimal_byte_parts.v2");
	*ID

[joseph-isaacs]

we really need to remove children from the vtable and only use slots