DependeNcy Injection

In .NET Core, "dependency injection" is a software design pattern where a class receives its dependencies (other objects it needs to function) from outside itself, rather than creating them internally 

1. Singleton: This creates only one instance of a class during the application's lifecycle. Every time you request this class, you get the same instance. Use it for classes that are expensive to create or maintain a common state throughout the application, like a database connection.

2. Scoped: Scoped instances are created once per client request. In a web application, for example, a new instance is created for each HTTP request but is shared across that request. Use it for services that need to maintain state within a request but not beyond it, like shopping cart in an e-commerce site.

3. Transient: Every time you request a transient class, a new instance is created. This is useful for lightweight, stateless services where each operation requires a clean and independent instance.