refactor: Add ProviderContext for a flexible storage directory

- Introduce ProviderContext class to decouple provider storage paths from absolute paths
- Add storage_dir attribute to StackRunConfig to accept CLI options
- Implement storage directory resolution with prioritized fallbacks:
  1. CLI option (--state-directory)
  2. Environment variable (LLAMA_STACK_STATE_DIR)
  3. Default distribution directory
- Standardize provider signatures to follow context, config, deps pattern
- Update provider implementations to use the new context-based approach
- Add comprehensive tests to verify state directory resolution

llama_stack/providers/inline/datasetio/localfs/datasetio.py

@@ -10,7 +10,7 @@ import pandas
 from llama_stack.apis.common.responses import PaginatedResponse
 from llama_stack.apis.datasetio import DatasetIO
 from llama_stack.apis.datasets import Dataset
-from llama_stack.providers.datatypes import DatasetsProtocolPrivate
+from llama_stack.providers.datatypes import DatasetsProtocolPrivate, ProviderContext
 from llama_stack.providers.utils.datasetio.url_utils import get_dataframe_from_uri
 from llama_stack.providers.utils.kvstore import kvstore_impl
 from llama_stack.providers.utils.pagination import paginate_records
@@ -53,7 +53,8 @@ class PandasDataframeDataset:
 
 
 class LocalFSDatasetIOImpl(DatasetIO, DatasetsProtocolPrivate):
-    def __init__(self, config: LocalFSDatasetIOConfig) -> None:
+    def __init__(self, context: ProviderContext, config: LocalFSDatasetIOConfig) -> None:
+        self.context = context
         self.config = config
         # local registry for keeping track of datasets within the provider
         self.dataset_infos = {}