HttpRetryOptions.from_json raises KeyError on wire payloads missing optional retry fields or using snake_case keys #351

Bug Description

In azure.durable_functions.http.models.HttpRetryOptions.from_json(), the deserializer assumes all optional fields are present as exact camelCase keys in the dictionary payload:

@classmethod
def from_json(cls, value: dict[str, Any]) -> "HttpRetryOptions":
    max_interval = value["maxRetryIntervalInMilliseconds"]
    timeout = value["retryTimeoutInMilliseconds"]
    return cls(
        first_retry_interval=timedelta(milliseconds=value["firstRetryIntervalInMilliseconds"]),
        max_number_of_attempts=value["maxNumberOfAttempts"],
        backoff_coefficient=value["backoffCoefficient"],
        max_retry_interval=timedelta(milliseconds=max_interval) if max_interval is not None else None,
        retry_timeout=timedelta(milliseconds=timeout) if timeout is not None else None,
        status_codes_to_retry=value.get("statusCodesToRetry"))

When a payload omits optional fields (such as maxRetryIntervalInMilliseconds, retryTimeoutInMilliseconds, or backoffCoefficient when default values were used, or when serialized across language boundaries), from_json() raises KeyError:

KeyError: 'maxRetryIntervalInMilliseconds'

Additionally, unlike DurableHttpResponse.from_json(), which defensively accepts both status_code and statusCode, HttpRetryOptions.from_json() does not support snake_case key naming (first_retry_interval_in_milliseconds, max_number_of_attempts, backoff_coefficient, etc.), failing with KeyError if snake_case dictionaries are supplied.

Expected Behavior

HttpRetryOptions.from_json() should safely parse dictionary payloads with missing optional fields, falling back to the class constructor's documented defaults (backoff_coefficient=1.0, max_retry_interval=timedelta(days=6), retry_timeout=None, status_codes_to_retry=None). It should also support both camelCase and snake_case key conventions defensively.