Bug: get_parameters_by_name with raise_on_error=False still raises on transform errors in the decrypt path, and caches None #8594

Expected Behaviour

With raise_on_error=False, a parameter whose transform fails is reported in _errors and does not stop the call, no matter whether it was fetched with GetParameter (decrypt) or GetParameters (batch). Failed transforms are not cached.

Current Behaviour

Two related problems in ssm.py:

1. _get_parameters_by_name_with_decrypt_option (:534) only catches GetParameterError, and BaseProvider.get hard-codes raise_on_transform_error=True, so a transform failure on a decrypted parameter raises TransformParameterError even in graceful mode. The same payload through the batch path returns None.
2. The batch path (:664) caches the None from a failed transform for max_age and does not list the name in _errors, while BaseProvider.get explicitly avoids caching None for that reason. A corrected parameter keeps returning None until the cache expires.

Code snippet

from botocore.config import Config
from botocore.stub import Stubber
from aws_lambda_powertools.utilities.parameters import SSMProvider

provider = SSMProvider(boto_config=Config(region_name="us-east-1"))
stub = Stubber(provider.client)
stub.add_response("get_parameter", {"Parameter": {"Name": "/a", "Value": "not json", "Type": "String", "Version": 1}}, {"Name": "/a", "WithDecryption": True})
stub.add_response("get_parameters", {"Parameters": [{"Name": "/b", "Value": "not json", "Type": "String", "Version": 1}]}, {"Names": ["/b"]})
stub.activate()

provider.get_parameters_by_name({"/a": {"decrypt": True}, "/b": {}}, transform="json", raise_on_error=False)
# TransformParameterError      expected: {'_errors': ['/a', '/b'], ...}

provider.get_parameters_by_name({"/b": {}}, transform="json", raise_on_error=False)
# {'_errors': [], '/b': None}  and provider.store now caches None for /b

Possible Solution

Catch TransformParameterError in the decrypt path and add the name to errors; in the batch path, skip add_to_cache when the transformed value is None and add the name to _errors.

Steps to Reproduce

Run the snippet above (it uses botocore.stub.Stubber, no AWS access needed).

Powertools for AWS Lambda (Python) version

latest

AWS Lambda function runtime

3.13

Packaging format used

PyPi

Debugging logs