Handle SDKContextClass client initialisation internally (#34146)

* Handle SDKContextClass `client` initialisation internally

Rather than via MatrixChat - this is predominantly for Lifecycle tests as they don't use a MatrixChat and it doesn't make much sense for this component to own this state.

* Fix tests

apps/web/test/unit-tests/modules/ExtrasApi-test.tsx

@@ -13,7 +13,7 @@ import { EventEmitter } from "events";
 import { stubClient } from "../../test-utils";
 import DMRoomMap from "../../../src/utils/DMRoomMap";
 import { SDKContext } from "../../../src/contexts/SDKContext";
-import { SDKContextClass } from "../../../src/contexts/SDKContextClass";
+import { TestSDKContext } from "../TestSDKContext.ts";
 import { ScopedRoomContextProvider } from "../../../src/contexts/ScopedRoomContext";
 import RoomContext, { type RoomContextType } from "../../../src/contexts/RoomContext";
 import MatrixClientContext from "../../../src/contexts/MatrixClientContext";
@@ -22,7 +22,7 @@ import { ModuleApi } from "../../../src/modules/Api";
 
 describe("ExtrasApi", () => {
     let client: MatrixClient;
-    let sdkContext: SDKContextClass;
+    let sdkContext: TestSDKContext;
     let room: Room;
     let roomContext: RoomContextType;
 
@@ -31,8 +31,8 @@ describe("ExtrasApi", () => {
         room = new Room("!test:room", client, "@alice:example.org", {
             pendingEventOrdering: PendingEventOrdering.Detached,
         });
-        sdkContext = new SDKContextClass();
-        sdkContext.client = client;
+        sdkContext = new TestSDKContext();
+        sdkContext._client = client;
         jest.spyOn(sdkContext.roomViewStore, "getRoomId").mockReturnValue(room.roomId);
 
         const mockRoomViewStore = new (class extends EventEmitter {