[feat][cp][DynamicMerge] Add lazy multi merge

[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 LocalMerge operator may start only a subset of the sources at a time to limit memory usage. Hence, it performs multiple partial sort-merge operations, each handling a subset of the merge sources. It spills the results produced by each subset and finishes the spill to ensure the order both within and across all spill files for each partial merge. Finally, creates a ConcatFilesSpillMergeStream for each group of spill files of each partial merge , setup a SpillMerger using those ConcatFilesSpillMergeStream to perform the final sort-merge of the outputs.

Parts of facebookincubator/velox#13260

Corresponding PR: facebookincubator/velox#13586

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.

  Click to view Benchmark Results

  Paste your google-benchmark or TPC-H results here.
  Before: 10.5s
  After:   8.2s  (+20%)
  

• 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: ...)

  Click to view Breaking Changes

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