Update gameplay logic/performance improvements

[1andDone]

• Updates gameplay logic
• Performance improvements
• Creates a dictionary that estimates the remaining decks, given how many cards are left in the shoe. This differs slightly from the previous implementation which used Python's built-in round function. This function rounded down when the fractional part was 0.5 (i.e. 338 / 52). The current implementation rounds up.
• Fixes minor bug in shoe.true_count method where 0 was sometimes showing up as negative 0
• Eliminates the StatsKey dataclass in favor of a tuple
• Updates the README