fix: Align Config aws_region default with documented default

The docstring, usage example, and test_config_defaults all state the
default region is us-west-2, but the code fell back to us-east-1 when
AWS_REGION was unset. CI sets only AWS_DEFAULT_REGION, so the test
failed once dependency installation was fixed (previously pytest died
at collection before reaching it). Align the code with the documented
default.

Author: Prince Grover

src/amazon_sop_bench/config.py

@@ -33,7 +33,7 @@ class Config:
 
     # AWS Settings
     aws_region: str = field(
-        default_factory=lambda: os.getenv("AWS_REGION", "us-east-1")
+        default_factory=lambda: os.getenv("AWS_REGION", "us-west-2")
     )
     aws_model_id: str = field(
         default_factory=lambda: os.getenv(