perf(duckdb): push down list length expressions

[mhk197]

Pushes DuckDB's list-length scalar function into the Vortex scan as the list_length expression, so lengths are computed from list offsets/sizes without materializing element values.

Stacked on #8495.

What

• Projection (SELECT len(list) / length(list) / array_length(list)): handled in try_from_projection_expression, gated on the projected column being List/FixedSizeList.
• Filter (WHERE array_length(list) >= k, also len/length): handled in try_from_bound_function + can_push_expression.
• Each maps to cast(list_length(col), i64) — DuckDB's len/array_length return BIGINT while list_length returns u64 — mirroring the existing strlen → byte_length pushdown.

len/length are overloaded with strings/bits, so the filter path needs the argument type to disambiguate. Added a small FFI accessor duckdb_vx_expr_get_return_type plus ExpressionRef::return_type(), and gate len/length/array_length on the bound child being LIST/ARRAY.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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

⚡ 1 improved benchmark
❌ 2 regressed benchmarks
✅ 1586 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	bitwise_not_vortex_buffer_mut[128]	186.1 ns	215.3 ns	-13.55%
❌	Simulation	bitwise_not_vortex_buffer_mut[1024]	246.4 ns	275.6 ns	-10.58%
⚡	Simulation	eq_i64_constant	318.3 µs	288.4 µs	+10.35%

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/duckdb-list-length-pushdown (9d94fe5) with mk/list-length (51b1a4c)}