Add deferrable mode to DynamoDBValueSensor

[harshhh817]

Adds the standard deferrable path to DynamoDBValueSensor, which currently only supports poke/reschedule modes and holds a worker slot while waiting.

• deferrable param (default from operators.default_deferrable, per provider convention); execute() defers to a new DynamoDBValueSensorTrigger, execute_complete() validates the trigger event.
• The trigger polls the item asynchronously. DynamoDBHook is resource-based but aiobotocore only exposes clients, so the trigger uses a client-type AwsBaseHook with low-level get_item and deserializes the attribute via boto3's TypeDeserializer — semantics identical to the sync poke() (ClientError tolerated, single value or iterable matched). This mirrors how EC2StateSensorTrigger handles the same client/resource split.
• Trigger registered in provider.yaml / get_provider_info.py; docs note added; unit tests for sensor deferral and trigger (serialization + async run paths).

The issue proposes DynamoDB Streams + SQS; I went with the async-polling trigger instead since it is the established pattern for the provider's deferrable sensors and requires no extra AWS infrastructure — happy to discuss if maintainers prefer the Streams-based design.

closes: #69051

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code)

Generated-by: Claude Code following the guidelines

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