get method
Returns the cached response for key, or null if expired or absent.
Implementation
String? get(String key) {
final entry = _entries[key];
if (entry == null) return null;
if (entry.isExpired) {
_entries.remove(key);
return null;
}
// Move to end for LRU semantics.
_entries.remove(key);
_entries[key] = entry;
return entry.response;
}