Property in LogEvent should not be overridden by scope

[huoshan12345]

trafficstars

fixes #271

NOTE: ExternalScopeProvider.ForEachScope processes scopes from outer to inner, which is the opposite of Serilog's scope traversal order. This fix implements ForEachScopeReversed and passes update: false to the method EnrichWithStateAndCreateScopeItem to ensure consistent behavior matching Serilog's expectations.