remove method
Removes the entry for key (if any) and returns its value, or null
if the key was absent or expired.
Implementation
T? remove(String? key) {
if (key == null) return null;
_expirationTimers.remove(key)?.cancel();
final item = _cache.remove(key);
if (item == null || item.isExpired) return null;
return item.value;
}