[feat][cp][DynamicMerge] Add Async SpillMerger in LocalMerge

[guhaiyan0221]

What problem does this PR solve?

Issue Number: close #191

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

Summary:
The current SpillMerger is single-thread sync mode using SpillMergeStream. It is beneficial to use multithreaded async mode to parallel the processing of merging on the consumer side and deserialization, and IO on the producer side. Create an async producer for each merge source using futures and callbacks, and execute them using the folly executor of the SpillConfig. Unify the consumer side by using SourceStream and LocalMergeSource in both SourceMerger and SpillMerger.

Part of facebookincubator/velox#13260

Corresponding PR: facebookincubator/velox#13634

Performance Impact

• No Impact: This change does not affect the critical path (e.g., build system, doc, error handling).
• Positive Impact: I have run benchmarks.
• Negative Impact: Explained below (e.g., trade-off for correctness).

Release Note

Please describe the changes in this PR

Release Note:

Release Note:
- Fixed a crash in `substr` when input is null.
- optimized `group by` performance by 20%.

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.