[AURON #2499] perf: avoid identity take in GenerateExec

[lyne7-sc]

Which issue does this PR close?

Closes #2499

Rationale for this change

Avoid redundant generated-array copies during non-outer GenerateExec.

What changes are included in this PR?

• Reuse generated output arrays directly when outer is false.
• Keep the existing take path for outer generation.
• Preserve the child-column take required to duplicate parent rows.

Are there any user-facing changes?

No. This is an internal performance improvement.

How was this patch tested?

Existed unit tests passed.

Benchmarks

The benchmark uses 10,000 input rows with 8 values per row. The reported values are averages of two runs.

Benchmark	Before	After	Improvement
explode_array_i32	0.625 ms	0.567 ms	9.3%
posexplode_array_i32	0.728 ms	0.617 ms	15.3%
explode_map_utf8_i32	1.156 ms	0.544 ms	53.0%
explode_array_i32_parent_null_gaps	0.551 ms	0.526 ms	4.5%

Was this patch authored or co-authored using generative AI tooling?

• Yes
• No

If yes, include: Generated-by: <tool name and version>

ASF guidance: https://www.apache.org/legal/generative-tooling.html