[cudf_polars] [MINOR] Configurable dask worker memory in benchmarks

[nirandaperera]

Description

This PR allows configuring dask worker memory in pdsh benchmarks. Only affects --cluster distributed without using --scheduler-address or --scheduler-file args (ie. when creating a LocalCUDACluster).

Discussion

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.