Fix clone comparer preservation and byok doc example

Preserve dictionary comparer in SessionConfig/ResumeSessionConfig
Clone() by checking for Dictionary<> and passing its Comparer.
Fix byok.md to use Task.FromResult<IList<ModelInfo>>() for the
updated delegate signature.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

docs/auth/byok.md

@@ -426,7 +426,7 @@ using GitHub.Copilot.SDK;
 
 var client = new CopilotClient(new CopilotClientOptions
 {
-    OnListModels = (ct) => Task.FromResult(new List<ModelInfo>
+    OnListModels = (ct) => Task.FromResult<IList<ModelInfo>>(new List<ModelInfo>
     {
         new()
         {

dotnet/src/Types.cs

@@ -1700,7 +1700,9 @@ protected SessionConfig(SessionConfig? other)
         Hooks = other.Hooks;
         InfiniteSessions = other.InfiniteSessions;
         McpServers = other.McpServers is not null
-            ? new Dictionary<string, McpServerConfig>(other.McpServers)
+            ? (other.McpServers is Dictionary<string, McpServerConfig> dict
+                ? new Dictionary<string, McpServerConfig>(dict, dict.Comparer)
+                : new Dictionary<string, McpServerConfig>(other.McpServers))
             : null;
         Model = other.Model;
         ModelCapabilities = other.ModelCapabilities;
@@ -1928,7 +1930,9 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
         Hooks = other.Hooks;
         InfiniteSessions = other.InfiniteSessions;
         McpServers = other.McpServers is not null
-            ? new Dictionary<string, McpServerConfig>(other.McpServers)
+            ? (other.McpServers is Dictionary<string, McpServerConfig> dict
+                ? new Dictionary<string, McpServerConfig>(dict, dict.Comparer)
+                : new Dictionary<string, McpServerConfig>(other.McpServers))
             : null;
         Model = other.Model;
         ModelCapabilities = other.ModelCapabilities;