Add tests for LaserCodeRegistry, clean up.

* Store a deque rather than an iterator so it can be pickled
* Remove mangling from staticmethod (and rename now that it's no longer
  a generator)
* Rename "get" to "alloc" to make the mutation clear
* Move to its own package (the changes I'm working on make this no
  longer mission generator specific)
* Remove useless exception class. It's never caught so the unique type
  isn't needed

game/lasercodes/__init__.py

@@ -0,0 +1 @@
+from .lasercoderegistry import LaserCodeRegistry

game/lasercodes/lasercoderegistry.py

@@ -0,0 +1,28 @@
+from collections import deque
+
+
+class LaserCodeRegistry:
+    def __init__(self) -> None:
+        self.allocated_codes: set[int] = set()
+        self.available_codes = LaserCodeRegistry._all_valid_laser_codes()
+
+    def alloc_laser_code(self) -> int:
+        try:
+            code = self.available_codes.popleft()
+            self.allocated_codes.add(code)
+            return code
+        except IndexError:
+            raise RuntimeError("All laser codes have been allocated")
+
+    @staticmethod
+    def _all_valid_laser_codes() -> deque[int]:
+        # Valid laser codes are as follows
+        # First digit is always 1
+        # Second digit is 5-7
+        # Third and fourth digits are 1 - 8
+        # We iterate backward (reversed()) so that 1687 follows 1688
+        q = deque(int(oct(code)[2:]) + 11 for code in reversed(range(0o1500, 0o2000)))
+
+        # We start with the default of 1688 and wrap around when we reach the end
+        q.rotate(-q.index(1688))
+        return q