Major refactor to the packages and include the gatherer.

Author: ZahidFKhan

src/test/java/com/github/streams/learn/b_advanced/gatherers/B_What is gatherer.md

@@ -2,7 +2,5 @@
 
 - The **Gatherer** is a new **intermediate operation** introduced to  the `java.util.stream.Stream` API in **Java 22**. 
 
-- Gatherer provides a way to implement **custom intermediate operations** that go beyond the fixed one-to-one (`map`), one-to-zero/one (`filter`), and one-to-many (`flatMap`) transformations.
-
 - It's designed to solve problems that were previously cumbersome or awkward to handle with the existing API by allowing the operation to maintain **internal state** and inspect **multiple upstream elements** before producing an output.
 - 

src/test/java/com/github/streams/learn/b_advanced/gatherers/C_When to use Custom gatherer.md

@@ -0,0 +1,5 @@
+When to use Custom Gatherers?
+
+1. When you're not able to solve the problem using filter, map or flatMap.
+2. When there exists no solution in the Gatherers even in latest JDK.
+3. When you're sure that's what you need.