Added new merge/combine function for the Saga

[idugalic]

Key Features of the Solution

The new function merge is introduced on the Saga component. It looks like a combine function, but these are different.

The two functions (combine and merge) explicitly handle different scenarios, which makes the code more readable and reduces potential runtime complexity.

combine:

Combines two sagas that operate on different event types (E and E2) into a new saga operating on Sum<E, E2>.
This is ideal for cases where you need to handle separate types of events independently.

merge:

Composes two sagas that operate on the same event type (E) into a new saga operating on E.
Ensures both sagas dispatch their own Commands/ActionResults in response to a shared event.