Flush underlying Store when a Cache is flushed

This ensures the buffered data in BufferedFileChannels is written to
disk even if close() is never called.

Signed-off-by: Graham <gpe@openrs2.org>

cache/src/main/kotlin/org/openrs2/cache/Cache.kt

@@ -227,6 +227,8 @@ public class Cache private constructor(
         for (archive in archives) {
             archive?.flush()
         }
+
+        store.flush()
     }
 
     /**