[Sept Sprint] Improve Blackjack

[ErikSchierboom]

This is part of our September Spring to get the Go Track in shape. Please read the Overview issue for more details. This exercise is unclaimed. To claim it, please comment below.

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Blackjack

• blackjack: streamline introduction #1556
• blackjack: move FirstTurn function from stub to tests file #1558

[andrerfcsantos]

I'll take this one too :)

[ErikSchierboom]

@andrerfcsantos We've removed the comparison requirement, as we're moving that to Cars Assemble (see #1611). I hope you didn't lose any work. If you had already started, you might want to indicate in the just linked issue that you could add the comparison concept to Cars Assemble