cache DTypes parsed from flatbuffers

[myrrc]

In clickbench queries, duckdb_reader_open accounts for 13% CPU time of the scan.
This is because for every file's field for every file Vortex parses DType from
a flatbuffer.

This change adds a cache of DTypes parsed from flatbuffers so among multiple
query iterations parsing is done exactly once per field

[robert3005]

Maybe FieldDType should have interior mutability and if we ever are forced to parse the view we mutate internal state and replace the view with the owned version?

[myrrc]

I've considered this option but it doesn't look neither less ugly nor more performant.

[codspeed-hq]

Merging this PR will regress 1 benchmark

⚠️ 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

⚡ 3 improved benchmarks
❌ 1 regressed benchmark
✅ 2195 untouched benchmarks
⏩ 206 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	random_i16[0.95]	77.2 µs	95.9 µs	-19.55%
⚡	WallTime	arrow_checked_add_u32_neon[16384]	20.4 µs	12.8 µs	+59.92%
⚡	Simulation	random_i16[0.8]	92.7 µs	75.3 µs	+22.98%
⚡	Simulation	allocate_drop_arrow[0]	456.9 ns	402.7 ns	+13.45%

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 myrrc/cache-parsed-dtype-fields (67e168c) with develop (3170657)}

Footnotes

1. 206 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. ↩

[myrrc]

Even if we have interior mutability, the issue is value() + cloning the field. If they refer to a flatbuffer view, then we need to re-parse the copied view, so we need an Arc to prevent that.

[robert3005]

I wish there was a nicer way but I can't think of one. You could come up with a way to apply expressions to dtypes but that still has to be progressively refined