Doctrine load from YAML (#3291)

This PR refactors the Doctrine class to load from YAML files in the
resources folder instead of being hardcoded as a step towards making
doctrines moddable (Issue #829).

I haven't added anything to the changelog as a couple of things should
get cleaned up first:
- As far as I can tell, the flags in the Doctrine class (cap, cas, sead
etc.) aren't used anywhere. Need to test further, and if they're truly
not used, will remove them.
- Probably need to update the Wiki

tests/data/test_doctrine.py

@@ -0,0 +1,43 @@
+import pytest
+
+from game.data.doctrine import Doctrine, GroundUnitProcurementRatios
+from game.data.units import UnitClass
+
+
+def test_ground_unit_procurement_ratios_empty() -> None:
+    r = GroundUnitProcurementRatios({})
+    for unit_class in UnitClass:
+        assert r.for_unit_class(unit_class) == 0.0
+
+
+def test_ground_unit_procurement_ratios_single_item() -> None:
+    r = GroundUnitProcurementRatios({UnitClass.TANK: 1})
+    for unit_class in UnitClass:
+        if unit_class == UnitClass.TANK:
+            assert r.for_unit_class(unit_class) == 1.0
+        else:
+            assert r.for_unit_class(unit_class) == 0.0
+
+
+def test_ground_unit_procurement_ratios_multiple_items() -> None:
+    r = GroundUnitProcurementRatios({UnitClass.TANK: 1, UnitClass.ATGM: 1})
+    for unit_class in UnitClass:
+        if unit_class in [UnitClass.TANK, UnitClass.ATGM]:
+            assert r.for_unit_class(unit_class) == 0.5
+        else:
+            assert r.for_unit_class(unit_class) == 0.0
+
+
+def test_ground_unit_procurement_ratios_from_dict() -> None:
+    r = GroundUnitProcurementRatios.from_dict({"Tank": 1, "ATGM": 1})
+    for unit_class in UnitClass:
+        if unit_class in [UnitClass.TANK, UnitClass.ATGM]:
+            assert r.for_unit_class(unit_class) == 0.5
+        else:
+            assert r.for_unit_class(unit_class) == 0.0
+
+
+def test_doctrine() -> None:
+    # This test checks for the presence of a doctrine named "modern" as this doctrine is used as a default
+    modern_doctrine = Doctrine.named("modern")
+    assert modern_doctrine.name == "modern"