Clean up namespaces (#410)

No meaningful code changes, just lots of namespace shuffling to have fewer namespaces and to put things in better namespaces.

src/ModelContextProtocol/Protocol/JsonRpcError.cs

@@ -0,0 +1,27 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Represents an error response message in the JSON-RPC protocol.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Error responses are sent when a request cannot be fulfilled or encounters an error during processing.
+/// Like successful responses, error messages include the same ID as the original request, allowing the
+/// sender to match errors with their corresponding requests.
+/// </para>
+/// <para>
+/// Each error response contains a structured error detail object with a numeric code, descriptive message,
+/// and optional additional data to provide more context about the error.
+/// </para>
+/// </remarks>
+public class JsonRpcError : JsonRpcMessageWithId
+{
+    /// <summary>
+    /// Gets detailed error information for the failed request, containing an error code, 
+    /// message, and optional additional data
+    /// </summary>
+    [JsonPropertyName("error")]
+    public required JsonRpcErrorDetail Error { get; init; }
+}