Accept a default value in Actor.getValue() #799

Crawlee v4's KeyValueStore.getValue(key, defaultValue) takes a default and has an overload that drops null from the return type (source). Actor.getValue(), its shortcut for the default store, takes only the key (instance, static). The Python SDK forwards a default_value (source). Add the same overloads to both the instance and static Actor.getValue().

✍️ Drafted by Claude Code