FFI: get scalars from arrays

[myrrc]

• Add vx_array_get_scalar method for retrieving vx_scalar.
• Add scalar's primitive, utf8, bool, and binary getters generated from a macro.
• Replace decimal scalar creation functions with a macro.
• Remove vx_array's primitive getters in favor of obtaining a vx_scarar.
• Add C++ API support for getting array's Scalar at index.
  Error propagation in C bindings #7483

[github-actions]

Polar Signals Profiling Results

Latest Run

Status	Commit	Job	Attempt	Link
🟢 Done	b1ac575		1	Explore Profiling Data

Previous Runs (1)

Status	Commit	Job	Attempt	Link
🟢 Done	3945f76		1	Explore Profiling Data

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[github-actions]

Verdict: No clear signal (low confidence)
Attributed Vortex impact: +2.5%
Engines: DataFusion Likely regression (+11.5%, medium confidence) · DuckDB No clear signal (-5.8%, low confidence)
Vortex (geomean): 0.954x ➖
Parquet (geomean): 0.942x ➖
Shifts: Parquet (control) -5.8% · Median polish -4.3%

How to read Verdict and Engines

• Verdict: Overall PR-level signal after subtracting baseline drift estimated from Parquet control rows. It can be Likely improvement, Likely regression, or No clear signal.
• Engines: Per-engine attribution. DataFusion is compared against DataFusion/Parquet controls; DuckDB is compared against DuckDB/Parquet controls. This answers whether each engine improved or regressed independently.
• Confidence: Based on directional consistency, share of rows above the noise floor, and control-run noise.

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datafusion / vortex-file-compressed (1.004x ➖, 0↑ 0↓)

name	PR b1ac575 (ns)	base 037b1a8 (ns)	ratio (PR/base)
vortex_q00/datafusion:vortex-file-compressed	9774512	10016685	0.98
vortex_q01/datafusion:vortex-file-compressed	6448746	6241940	1.03

datafusion / parquet (0.901x ➖, 1↑ 0↓)

name	PR b1ac575 (ns)	base 037b1a8 (ns)	ratio (PR/base)
vortex_q00/datafusion:parquet	20056827	21628324	0.93
vortex_q01/datafusion:parquet 🚀	4574698	5231454	0.87

duckdb / vortex-file-compressed (0.929x ➖, 0↑ 0↓)

name	PR b1ac575 (ns)	base 037b1a8 (ns)	ratio (PR/base)
vortex_q00/duckdb:vortex-file-compressed	10144766	10577988	0.96
vortex_q01/duckdb:vortex-file-compressed	5933116	6588883	0.90

duckdb / parquet (0.986x ➖, 0↑ 0↓)

name	PR b1ac575 (ns)	base 037b1a8 (ns)	ratio (PR/base)
vortex_q00/duckdb:parquet	23406979	23594326	0.99
vortex_q01/duckdb:parquet	9363326	9549441	0.98

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No file size changes detected.

[myrrc]

I've checked again, and I think we want a more gradual change.

We do want to be able to get a scalar for an array, but we can't replace current getters with an intermediate vx_scalar:

1. for bool, we would pay the price of allocating a scalar for every item. This is non-performant, but acceptable, and can be solved by ffi: create bool arrays #8899
2. For strings, however, we can't have an intermediate Scalar because the vx_view's now borrow from a scalar, and C++ api's bulk access would become UB.

I've removed the primitive accessors here.