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/Types/RequestParamsMetadata.cs

@@ -1,23 +0,0 @@
-using ModelContextProtocol.Protocol.Messages;
-using System.Text.Json.Serialization;
-
-namespace ModelContextProtocol.Protocol.Types;
-
-/// <summary>
-/// Provides metadata related to the request that provides additional protocol-level information.
-/// </summary>
-/// <remarks>
-/// This class contains properties that are used by the Model Context Protocol
-/// for features like progress tracking and other protocol-specific capabilities.
-/// </remarks>
-public class RequestParamsMetadata
-{
-    /// <summary>
-    /// Gets or sets an opaque token that will be attached to any subsequent progress notifications.
-    /// </summary>
-    /// <remarks>
-    /// The receiver is not obligated to provide these notifications.
-    /// </remarks>
-    [JsonPropertyName("progressToken")]
-    public ProgressToken? ProgressToken { get; set; } = default!;
-}