Return cached room members before fetching new ones, do it in batches (#2274)

* Use cached users from the Rust SDK.

Also lazy load received users by batches.

* Create `RoomMemberListFetcher` to wrap all the room member loading logic

* Ensure we clear `RoomMember` Rust references if the fetching coroutine is canceled

libraries/matrix/impl/build.gradle.kts

@@ -53,4 +53,5 @@ dependencies {
     testImplementation(libs.test.truth)
     testImplementation(projects.libraries.matrix.test)
     testImplementation(libs.coroutines.test)
+    testImplementation(libs.test.turbine)
 }