fix: location constraint for default region (#44)

Fixes failure where LocationConstraint is not accepted when region is
us-east-1 (default)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Automatically applies the "us-east-1" region when no region is
specified, ensuring a consistent default configuration.
- **Refactor**
- Simplified the bucket creation process by streamlining how the region
is handled, resulting in improved consistency when interacting with
storage services.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: jakevc

snakemake_storage_plugin_s3/__init__.py

@@ -27,6 +27,8 @@
 )
 from snakemake_interface_storage_plugins.common import Operation
 
+DEFAULT_REGION = "us-east-1"
+
 
 # Optional:
 # Define settings for your storage plugin (e.g. host url, credentials).
@@ -58,7 +60,7 @@ class StorageProviderSettings(StorageProviderSettingsBase):
         },
     )
     region: Optional[str] = field(
-        default=None,
+        default=DEFAULT_REGION,
         metadata={
             "help": "region constraint for the S3 storage",
             "env_var": True,
@@ -325,12 +327,12 @@ def store_object(self):
         # Ensure that the object is stored at the location specified by
         # self.local_path().
         if not self.bucket_exists():
-            location_config = {}
-            if self.provider.settings.region is not None:
-                location_config = {"LocationConstraint": self.provider.settings.region}
-            self.provider.s3c.create_bucket(
-                Bucket=self.bucket, CreateBucketConfiguration=location_config
-            )
+            create_bucket_params = {"Bucket": self.bucket}
+            if self.provider.settings.region != DEFAULT_REGION:
+                create_bucket_params["CreateBucketConfiguration"] = {
+                    "LocationConstraint": self.provider.settings.region
+                }
+            self.provider.s3c.create_bucket(**create_bucket_params)
 
         if self.local_path().is_dir():
             self._is_dir = True