Generic Sky Box

Finish the generic class Box<T>:

• getValue() returns the value the box was created with.
• map(fn) takes a function from T to U and returns a new Box<U> holding fn(value). The original box must not change.

Then write boxPipeline(start): put start in a box, map it with "add 1", then map the result with "double it", and return the final value.