Refactor the custom helpers into their own files

module/helpers/detailsExpanded.mjs

@@ -0,0 +1,11 @@
+/**
+ * Checks if the specified collapseId is currently open, so that during re-renders
+ * it remains open or closed.
+ *
+ * @param {Set<string>} expanded A set indicating what collapseIds are expanded
+ * @param {string} collapseId The collapseId to check for
+ * @returns {"open"|null} The HTML insertion indicating the details is expanded
+ */
+export function detailsExpanded(expanded, collapseId) {
+	return expanded.has(collapseId) ? "open" : null;
+};