Default JSON-based cookie serializer. NOTE: this implementation serializes `Map` polymorphically using the reflection-based `System.Text.Json` APIs. It is therefore NOT compatible with .NET Native AOT or aggressive trimming. Consumers targeting AOT must implement `CookieSerialiser` themselves over a closed payload schema (e.g. using a `JsonSerializerContext` source generator) and assign it to `SuaveConfig.cookieSerialiser`. The historical name `BinaryFormatterSerialiser` is preserved for source compatibility; the underlying engine has been `System.Text.Json` for a while.