Fix build failures after @github/copilot update

SessionModelSwitchToParams record gained a new reasoningSummary field,
requiring callers to pass 5 arguments instead of 4. Updated both call
sites in CopilotSession to pass null for the new reasoningSummary
parameter.

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

Author: github-actions[bot]

src/main/java/com/github/copilot/sdk/CopilotSession.java

@@ -1657,7 +1657,7 @@ public CompletableFuture<Void> abort() {
      */
     public CompletableFuture<Void> setModel(String model, String reasoningEffort) {
         ensureNotTerminated();
-        return getRpc().model.switchTo(new SessionModelSwitchToParams(sessionId, model, reasoningEffort, null))
+        return getRpc().model.switchTo(new SessionModelSwitchToParams(sessionId, model, reasoningEffort, null, null))
                 .thenApply(r -> null);
     }
 
@@ -1706,7 +1706,7 @@ public CompletableFuture<Void> setModel(String model, String reasoningEffort,
             generatedCapabilities = new ModelCapabilitiesOverride(supports, limits);
         }
         return getRpc().model
-                .switchTo(new SessionModelSwitchToParams(sessionId, model, reasoningEffort, generatedCapabilities))
+                .switchTo(new SessionModelSwitchToParams(sessionId, model, reasoningEffort, null, generatedCapabilities))
                 .thenApply(r -> null);
     }