Implement coffee machine program and tests (MIL-002)

Add the Menu, MenuItem, CoffeeMaker and MoneyMachine classes with the
assignment's method names, and a main loop that supports drink names,
report and off. Resources are checked before payment, and payment
before the drink is made.

Move drink prices, ingredient amounts and all message text into
constants.py. Add 25 pytest tests for every class and the main loop,
and record the review against QC-PY-001 as RC-007.

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6
Closes #6
Closes #7
Closes #8
Closes #9
Closes #10
Closes #11

src/coffee_machine/money_machine.py

@@ -0,0 +1,59 @@
+"""! @file
+@brief The part of the machine that takes coins and keeps the profit.
+"""
+
+from coffee_machine import constants
+
+
+class MoneyMachine:
+    """! @brief Processes coins, gives change and keeps the profit."""
+
+    def __init__(self) -> None:
+        """! @brief Start with the initial profit and no money received."""
+        self.profit: float = constants.INITIAL_PROFIT
+        self.money_received: float = 0.0
+
+    def report(self) -> None:
+        """! @brief Print the money in the machine."""
+        print(f"Money: {constants.CURRENCY}{self.profit:.{constants.MONEY_DECIMALS}f}")
+
+    def process_coins(self) -> float:
+        """! @brief Ask for each coin type and add up the value.
+
+        @return The total value of the coins inserted, in dollars.
+        """
+        print(constants.MSG_INSERT_COINS)
+        total = 0.0
+        for coin, value in constants.COIN_VALUES.items():
+            total += self._ask_count(coin) * value
+        self.money_received = round(total, constants.MONEY_DECIMALS)
+        return self.money_received
+
+    def make_payment(self, cost: float) -> bool:
+        """! @brief Take coins for a drink, give change or refund.
+
+        @param cost The price of the drink in dollars.
+        @return True when enough money was inserted.
+        """
+        self.process_coins()
+        if self.money_received < cost:
+            print(constants.MSG_NOT_ENOUGH_MONEY)
+            self.money_received = 0.0
+            return False
+        change = round(self.money_received - cost, constants.MONEY_DECIMALS)
+        if change > 0:
+            print(
+                constants.MSG_CHANGE.format(currency=constants.CURRENCY, change=change)
+            )
+        self.profit += cost
+        self.money_received = 0.0
+        return True
+
+    @staticmethod
+    def _ask_count(coin: str) -> int:
+        """! @brief Ask how many coins of one type until a valid count is given."""
+        while True:
+            answer = input(constants.MSG_COIN_PROMPT.format(coin=coin))
+            if answer.strip().isdigit():
+                return int(answer)
+            print(constants.MSG_INVALID_COUNT)