ItemCF召回方法的并行

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The issue title mentions parallelizing ItemCF recall in AutoX, a Python automl tool for tabular data. Look for ItemCF implementation in the codebase, likely in recommendation or collaborative filtering modules. Investigate existing data processing pipelines to identify where parallelism can be added, possibly using multiprocessing or distributed computing frameworks. Check test files for ItemCF to understand the expected behavior and ensure changes maintain correctness.

索引モデルが issue の本文から書いたものです。