Add support for comma separated strings

Signed-off-by: Vibhu Jawa <vibhujawa@gmail.com>

dask_cuda/local_cuda_cluster.py

@@ -143,10 +143,11 @@ class LocalCUDACluster(LocalCluster):
             The asynchronous allocator requires CUDA Toolkit 11.2 or newer. It is also
             incompatible with RMM pools and managed memory. Trying to enable both will
             result in an exception.
-    rmm_allocator_external_lib_list: list or None, default None
+    rmm_allocator_external_lib_list: str, list or None, default None
         List of external libraries for which to set RMM as the allocator.
-        Supported options are: ``["torch", "cupy"]``. If ``None``, no external
-        libraries will use RMM as their allocator.
+        Supported options are: ``["torch", "cupy"]``. Can be a comma-separated string
+        (like ``"torch,cupy"``) or a list of strings (like ``["torch", "cupy"]``).
+        If ``None``, no external libraries will use RMM as their allocator.
     rmm_release_threshold: int, str or None, default None
         When ``rmm.async is True`` and the pool size grows beyond this value, unused
         memory held by the pool will be released at the next synchronization point.
@@ -271,15 +272,17 @@ def __init__(
         if n_workers < 1:
             raise ValueError("Number of workers cannot be less than 1.")
 
-        if rmm_allocator_external_lib_list is not None and not isinstance(
-            rmm_allocator_external_lib_list, list
-        ):
-            raise ValueError(
-                "rmm_allocator_external_lib_list must be a list of strings. "
-                "Valid examples: ['torch'], ['cupy'], or ['torch', 'cupy']. "
-                f"Received: {type(rmm_allocator_external_lib_list)} "
-                f"with value: {rmm_allocator_external_lib_list}"
-            )
+        if rmm_allocator_external_lib_list is not None:
+            if isinstance(rmm_allocator_external_lib_list, str):
+                rmm_allocator_external_lib_list = [
+                    v.strip() for v in rmm_allocator_external_lib_list.split(",")
+                ]
+            elif not isinstance(rmm_allocator_external_lib_list, list):
+                raise ValueError(
+                    "rmm_allocator_external_lib_list must be either a comma-separated "
+                    "string or a list of strings. Examples: 'torch,cupy' "
+                    "or ['torch', 'cupy']"
+                )
 
         # Set nthreads=1 when parsing mem_limit since it only depends on n_workers
         logger = logging.getLogger(__name__)