Add TemporaryMatrixClient interface

This is an abstraction over an actual unauthenticated `Client` from the SDK that implements `GetUrlResolver`, and is supposed to be short-lived.

With this, we can use the SDK network stack to perform arbitrary GET url operations.

The `AutoCloseable` implementation makes it easier to clean up any leftover local config after using this temporary client.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/TemporaryMatrixClient.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.matrix.api
+
+import java.lang.AutoCloseable
+
+/**
+ * A Matrix client in an 'unauthenticated' state that can still be used to resolve URLs.
+ *
+ * Note: this client implements an [AutoCloseable] interface, so using [AutoCloseable.close] or [AutoCloseable.use] will clean up any resources associated
+ * with it, such as temporary files.
+ */
+interface TemporaryMatrixClient : GetUrlResolver, AutoCloseable

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/TemporaryMatrixClientFactory.kt

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.matrix.api
+
+/**
+ * Factory to create a temporary [TemporaryMatrixClient] for a given home server URL.
+ */
+interface TemporaryMatrixClientFactory {
+    suspend fun createTemporaryMatrixClient(homeServerUrl: String): Result<TemporaryMatrixClient>
+}