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/Argument.cs

@@ -1,29 +0,0 @@
-using System.Text.Json.Serialization;
-
-namespace ModelContextProtocol.Protocol.Types;
-
-/// <summary>
-/// Represents an argument used in completion requests to provide context for auto-completion functionality.
-/// </summary>
-/// <remarks>
-/// This class is used when requesting completion suggestions for a particular field or parameter.
-/// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
-/// </remarks>
-public class Argument
-{
-    /// <summary>
-    /// Gets or sets the name of the argument being completed.
-    /// </summary>
-    [JsonPropertyName("name")]
-    public string Name { get; set; } = string.Empty;
-
-    /// <summary>
-    /// Gets or sets the current partial text value for which completion suggestions are requested.
-    /// </summary>
-    /// <remarks>
-    /// This represents the text that has been entered so far and for which completion
-    /// options should be generated.
-    /// </remarks>
-    [JsonPropertyName("value")]
-    public string Value { get; set; } = string.Empty;
-}