Implement the RowFn execution backend

[connortsui20]

Rationale for this change

• Tracking issue: Tracking Issue: Execute RowFn over Vortex arrays #9130
• API tracking: Tracking Issue: Define the RowFn API #9129
• Epic: Epic: Row-oriented scalar functions #9128

Implements execution for the contracts in #9386.

What changes are included in this PR?

Adds batch validity and constant handling, dense and valid-only strategies, prepared row loops, sink execution, reducer handling, and output validation. It completes the execute_rows path in the blanket adapter introduced by #9386.

What APIs are changed? Are there any user-facing changes?

Adds execution internals within the existing unstable_row_fns boundary. There are no stable API changes.

[codspeed-hq]

Merging this PR will degrade performance by 26.3%

⚠️ 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.

❌ 2 regressed benchmarks
✅ 1992 untouched benchmarks
⏩ 89 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	decode_varbin[(1000, 4)]	60.3 µs	97.4 µs	-38.06%
❌	WallTime	words_gather_scalar[65536]	8.2 µs	9.4 µs	-12.31%

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 ct/row-fn-framework (6ddd036) with ct/row-fn-types (707d106)²}

Footnotes

1. 89 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. ↩

2. No successful run was found on ct/row-fn-types (c02fe9d) during the generation of this report, so 0f50f99 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩