Add @Subscribe annotation

[no changelog]

symbols/src/main/kotlin/Subscribe.kt

@@ -0,0 +1,12 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Linnea Gräf <nea@nea.moe>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package moe.nea.firmament.annotations
+
+@Target(AnnotationTarget.FUNCTION)
+@Retention(AnnotationRetention.SOURCE)
+annotation class Subscribe
+