⚡ Bolt: Optimize Hash Join for Single-Batch Build Side

[google-labs-jules]

• 💡 What: This optimization adds a fast path to the collect_left_input function in the HashJoinExec operator. It avoids the expensive concat_batches operation when the build side of the join consists of a single RecordBatch.
• 🎯 Why: The concat_batches function allocates new memory and copies data, which is unnecessary overhead when there's only one batch. This change improves performance for a common join scenario.
• 📊 Impact: Improves hash join performance by reducing memory allocation and CPU usage for single-batch build-side inputs.
• 🔬 Measurement: This can be verified by observing improved performance in benchmarks involving joins where the build side is small enough to fit into a single batch.

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PR created automatically by Jules for task 4148456866613629032 started by @Dandandan

[google-labs-jules]

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