simplified code across the app and consolidated duplicated helpers

lib/view/pages/files/data/webdav_path.dart

@@ -0,0 +1,26 @@
+// Paths relative to the WebDAV root, as used by `CacheableFile.path`: no
+// leading slash, folders end with '/', the root folder is ''.
+
+final RegExp _edgeSlashes = RegExp(r'^/+|/+$');
+
+List<String> webdavSegmentsOf(String path) {
+  final stripped = path.replaceAll(_edgeSlashes, '');
+  return stripped.isEmpty ? [] : stripped.split('/');
+}
+
+List<String> webdavParentSegmentsOf(String path) {
+  final segments = webdavSegmentsOf(path);
+  if (segments.isNotEmpty) segments.removeLast();
+  return segments;
+}
+
+String webdavFolderPath(List<String> segments) =>
+    segments.isEmpty ? '' : '${segments.join('/')}/';
+
+String webdavJoin(String folder, String name, {required bool isDirectory}) =>
+    isDirectory ? '$folder$name/' : '$folder$name';
+
+/// Folder key used by `ListFilesCache` and `FilesBloc`: no leading or
+/// trailing slash, root is '/'.
+String listFilesCacheKey(List<String> segments) =>
+    segments.isEmpty ? '/' : segments.join('/');