refactor: isolate bitpacked v1 serde in the plugin

[mhk197]

Move serialization and deserialization of fastlanes.bitpacked into BitPackedPlugin, shared with the external-patches adapter. The plugin owns the protobuf metadata and wire validation.

The VTable retains only the required error-returning serde methods and in-memory array validation.

[codspeed]

Merging this PR will regress 3 benchmarks

⚠️ 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

⚡ 5 improved benchmarks
❌ 3 regressed benchmarks
✅ 2200 untouched benchmarks
⏩ 293 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	decode_primitives[f32, (1000, 512)]	42.3 µs	64.6 µs	-34.56%
❌	Simulation	take_fsl_u32_random[128, 100]	208.3 µs	237.2 µs	-12.18%
❌	Simulation	take_fsl_f16_random[256, 100]	204.9 µs	230.5 µs	-11.11%
⚡	Simulation	take_fsl_u32_random[16, 100]	165.8 µs	125.9 µs	+31.66%
⚡	WallTime	dbp_assemble_kernel_avx512[(I128, 1024)]	546 ns	465 ns	+17.42%
⚡	Simulation	take_fsl_nullable_random[16, 100]	187.7 µs	165.4 µs	+13.49%
⚡	WallTime	dbp_assemble_kernel_avx2[(I128, 1024)]	561 ns	502 ns	+11.75%
⚡	WallTime	dbp_assemble_kernel_narrow_msp_avx2[(I128, 1024)]	699 ns	626 ns	+11.66%

Tip

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

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_{Comparing mk/bitpacked-stack-01-wire-boundary (349b196) with develop (c3ade49)}

Footnotes

1. 293 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. ↩