fix: Fix NightscoutAPI fetchLastGlucose

[bastiaanv]

Currently, if you want to backfill via Nightscout or use Nightscout as a CGM, you will get the following warning:
Glucose fetching error: The data couldn’t be read because it isn’t in the correct format.

This is due to the property sgv being marked as Int but Nightscout returns it as a double/decimal.
This PR fixes this issue by first trying to parse the property as an Int and then try to parse as Double (with casting to Int) and only after that throw an error.

Debugged error thrown by swift:
dataCorrupted - Context(codingPath: [], debugDescription: \"The given data was not valid JSON.\", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 \"Number 241.2 is not representable in Swift.\" UserInfo={NSDebugDescription=Number 241.2 is not representable in Swift.}))

Nightscout API response (partial):

[
  {
    "_id": "669d5a7a8de7c615a2661098",
    "device": "MiaomiaoClient",
    "date": 1721588346033.709,
    "type": "sgv",
    "direction": "Flat",
    "trend": 4,
    "isCalibration": false,
    "sgv": 241.2,
    "dateString": "2024-07-21T18:59:06.000Z",
    "utcOffset": 0,
    "sysTime": "2024-07-21T18:59:06.000Z"
  },
]

Code to debug the error:

return service.run(request)
            .retry(Config.retryCount)
            .decode(type: [BloodGlucose].self, decoder: JSONCoding.decoder)
            .catch { error -> AnyPublisher<[BloodGlucose], Swift.Error> in
                warning(.nightscout, "Glucose fetching error: \(error.localizedDescription)")
                var str = ""

                switch error {
                case let DecodingError.keyNotFound(key, context):
                    str = "keyNotFound - key: \(key)"
                case let DecodingError.dataCorrupted(context):
                    str = "dataCorrupted - \(context)"
                case let DecodingError.valueNotFound(value, context):
                    str = "valueNotFound - value: \(value)"
                case let DecodingError.typeMismatch(type, context):
                    str = "typeMismatch - type: \(type)"
                default:
                    str = "UNKNWON"
                }
                return Just([]).setFailureType(to: Swift.Error.self).eraseToAnyPublisher()
            }
            .map { glucose in
                glucose
                    .map {
                        var reading = $0
                        reading.glucose = $0.sgv
                        return reading
                    }
            }
            .eraseToAnyPublisher()

close #605