Use System.Net.ServerSentEvents

[HavenDV]

https://github.com/PederHP/mcpdotnet/pull/32/files

[HavenDV]

Fixed on main. SSE generation now uses System.Net.ServerSentEvents.SseParser in src/libs/AutoSDK/Sources/Sources.Methods.cs, and snapshot tests explicitly reference the System.Net.ServerSentEvents package.