preload method
Loads and caches each animation.
Implementation
Future<Map<String, PrismLottie>> preload(List<String> paths) async {
for (final path in paths) {
if (_cache.containsKey(path)) continue;
final json = await rootBundle.loadString(path);
_cache[path] = PrismLottie.fromJson(json);
}
return Map.unmodifiable(_cache);
}