Fix memory leak in `config-parquet-and-info`: do not store pq.ParquetFIle objects in memory
should fix [this](https://github.com/huggingface/datasets-server/issues/2552)

\+ i added test for `fill_builder_info` with multiple parquet files (seems that all other tests for this worker use only 1) 
Fix memory leak in `config-parquet-and-info`: do not store pq.ParquetFIle objects in memory: should fix [this](https://github.com/huggingface/datasets-server/issues/2552)

\+ i added test for `fill_builder_info` with multiple parquet files (seems that all other tests for this worker use only 1) 