✨ Add file sink rotation and retention

bitlogger/file_backend_stub.mbt

@@ -26,6 +26,26 @@ fn close_file_handle_internal(handle : FileHandle) -> Bool {
   false
 }
 
+fn file_size_internal(handle : FileHandle) -> Int {
+  ignore(handle)
+  0
+}
+
+fn rename_file_internal(from_path : String, to_path : String) -> Bool {
+  ignore(from_path)
+  ignore(to_path)
+  false
+}
+
+fn remove_file_internal(path : String) -> Bool {
+  ignore(path)
+  false
+}
+
+fn string_byte_length_internal(content : String) -> Int {
+  content.length()
+}
+
 fn native_files_supported_internal() -> Bool {
   false
 }