fix: add us-west-2 to Nova supported regions

[pilgd-aws]

Problem

NOVA_REGIONS in finetune_utils.py was hardcoded to ['us-east-1'], causing all trainers (SFTTrainer, DPOTrainer, RLVRTrainer, RLAIFTrainer) to raise a ValueError when instantiated in us-west-2, even though the SageMaker service supports Nova fine-tuning there.

Fix

Added us-west-2 to NOVA_REGIONS. Updated test__validate_model_region_availability_nova_invalid_region to use eu-west-1 (a genuinely unsupported region) and added us-west-2 to the valid-region test.

Testing

Nova fine-tuning in us-west-2 (PDX) has been verified working via the SageMaker console UI workflow — the PySDK should match service-level availability.

Unit tests run locally:

AWS_DEFAULT_REGION=us-east-1 python -m pytest tests/unit/train/common_utils/test_finetune_utils.py -v
55 passed in 3.08s

[mollyheamazon]

Last PR test run looks good: https://github.com/aws/sagemaker-python-sdk/actions/runs/24744360572