Singleton Design Pattern

The Singleton pattern ensures that a class has only one instance throughout the lifetime of a program, and provides a global access point to that instance.

This is useful for managing shared resources — loggers, configuration managers, and database connection pools are all commonly implemented as Singletons.

Implement the Singleton class such that:

• Only one instance of Singleton is ever created
• Every call to Singleton() returns the same object
• The identity check Singleton() is Singleton() always returns True

Also implement Singleton.reset() — a classmethod that clears the stored instance. This is used for testing purposes only and would not appear in a production implementation.

Note: This is the single-threaded implementation. Thread safety is not required here.

Constraints:

• Do not use any external libraries
• Your implementation must override __new__
• reset() must allow a fresh instance to be created after it is called