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/Client/SseClientTransportOptions.cs

@@ -0,0 +1,65 @@
+namespace ModelContextProtocol.Client;
+
+/// <summary>
+/// Provides options for configuring <see cref="SseClientTransport"/> instances.
+/// </summary>
+public record SseClientTransportOptions
+{
+    /// <summary>
+    /// Gets or sets the base address of the server for SSE connections.
+    /// </summary>
+    public required Uri Endpoint
+    {
+        get;
+        init
+        {
+            if (value is null)
+            {
+                throw new ArgumentNullException(nameof(value), "Endpoint cannot be null.");
+            }
+            if (!value.IsAbsoluteUri)
+            {
+                throw new ArgumentException("Endpoint must be an absolute URI.", nameof(value));
+            }
+            if (value.Scheme != Uri.UriSchemeHttp && value.Scheme != Uri.UriSchemeHttps)
+            {
+                throw new ArgumentException("Endpoint must use HTTP or HTTPS scheme.", nameof(value));
+            }
+
+            field = value;
+        }
+    }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether to use "Streamable HTTP" for the transport rather than "HTTP with SSE". Defaults to false.
+    /// <see href="https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http">Streamable HTTP transport specification</see>.
+    /// <see href="https://modelcontextprotocol.io/specification/2024-11-05/basic/transports#http-with-sse">HTTP with SSE transport specification</see>.
+    /// </summary>
+    public bool UseStreamableHttp { get; init; }
+
+    /// <summary>
+    /// Gets a transport identifier used for logging purposes.
+    /// </summary>
+    public string? Name { get; init; }
+
+    /// <summary>
+    /// Gets or sets a timeout used to establish the initial connection to the SSE server. Defaults to 30 seconds.
+    /// </summary>
+    /// <remarks>
+    /// This timeout controls how long the client waits for:
+    /// <list type="bullet">
+    ///   <item><description>The initial HTTP connection to be established with the SSE server</description></item>
+    ///   <item><description>The endpoint event to be received, which indicates the message endpoint URL</description></item>
+    /// </list>
+    /// If the timeout expires before the connection is established, a <see cref="TimeoutException"/> will be thrown.
+    /// </remarks>
+    public TimeSpan ConnectionTimeout { get; init; } = TimeSpan.FromSeconds(30);
+
+    /// <summary>
+    /// Gets custom HTTP headers to include in requests to the SSE server.
+    /// </summary>
+    /// <remarks>
+    /// Use this property to specify custom HTTP headers that should be sent with each request to the server.
+    /// </remarks>
+    public Dictionary<string, string>? AdditionalHeaders { get; init; }
+}