Optimize collect_list for fixed-width and varchar types

[taiyang-li]

What problem does this PR solve?

Issue Number: close #xxx

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 🚀 Performance improvement (optimization)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)
• 🔨 Refactoring (no logic changes)
• 🔧 Build/CI or Infrastructure changes
• 📝 Documentation only

Description

This PR optimizes Spark-compatible collect_list aggregation in two paths.

For fixed-width primitive inputs, such as BIGINT, INT, DOUBLE, etc., collect_list now uses a typed accumulator backed by contiguous typed storage instead of the generic ValueList + ContainerRowSerde path. This avoids per-value generic row serialization/deserialization and reduces accumulator overhead for fixed-width values.

For VARCHAR / VARBINARY inputs, this PR keeps the existing ValueList accumulator layout, but adds a string-specific fast path for appending and reading string values. The serialized layout remains length + bytes, while avoiding the broader ContainerRowSerde dispatch path for string collect_list accumulation and extraction.

Together, these changes improve both fixed-width and string collect_list workloads, including Spark-style partial aggregation -> final aggregation plans.

Performance Impact

Benchmark target:

./_build/Release/bolt/functions/sparksql/benchmarks/bolt_collect_list_aggregate_bm

Before:

============================================================================
[...]rks/CollectListAggregateBenchmark.cpp     relative  time/iter   iters/s
============================================================================
collect_list_bigint_partial_final_plan                     18.83ms     53.11
collect_list_string_partial_final_plan                     26.87ms     37.21

After:

============================================================================
[...]rks/CollectListAggregateBenchmark.cpp     relative  time/iter   iters/s
============================================================================
collect_list_bigint_partial_final_plan                      3.51ms    285.12
collect_list_string_partial_final_plan                     12.09ms     82.70

Summary:

Benchmark	Before	After	Speedup
collect_list_bigint_partial_final_plan	18.83ms	3.51ms	5.36x
collect_list_string_partial_final_plan	26.87ms	12.09ms	2.22x

This shows a significant improvement for both primitive and string collect_list in a plan shape that includes both partial and final aggregation.

Checklist (For Author)

• I have added/updated unit tests (ctest).
• I have verified the code with local build (Release/Debug).
• I have run clang-format / linters.
• (Optional) I have run Sanitizers (ASAN/TSAN) locally for complex C++ changes.
• No need to test or manual test.

Breaking Changes

• No

• Yes (Description: ...)

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  Breaking Changes:
  - Description of the breaking change.
  - Possible solutions or workarounds.
  - Any other relevant information.