feat: Implement FOV enum and layer draw_fov for #114 and #113

Phase 1 - FOV Enum System:
- Create PyFOV.h/cpp with mcrfpy.FOV IntEnum (BASIC, DIAMOND, SHADOW, etc.)
- Add mcrfpy.default_fov module property initialized to FOV.BASIC
- Add grid.fov and grid.fov_radius properties for per-grid defaults
- Remove deprecated module-level FOV_* constants (breaking change)

Phase 2 - Layer Operations:
- Implement ColorLayer.fill_rect(pos, size, color) for rectangle fills
- Implement TileLayer.fill_rect(pos, size, index) for tile rectangle fills
- Implement ColorLayer.draw_fov(source, radius, fov, visible, discovered, unknown)
  to paint FOV-based visibility on color layers using parent grid's TCOD map

The FOV enum uses Python's IntEnum for type safety while maintaining
backward compatibility with integer values. Tests updated to use new API.

Addresses #114 (FOV enum), #113 (layer operations)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/test_tcod_complete.py

@@ -37,13 +37,13 @@ def run_tests():
     # Test 3: Field of View
     print("Test 3: Field of View Algorithms")
     
-    # Test different algorithms
+    # Test different algorithms (using new mcrfpy.FOV enum)
     algorithms = [
-        ("Basic", mcrfpy.FOV_BASIC),
-        ("Diamond", mcrfpy.FOV_DIAMOND),
-        ("Shadow", mcrfpy.FOV_SHADOW),
-        ("Permissive", mcrfpy.FOV_PERMISSIVE_2),
-        ("Restrictive", mcrfpy.FOV_RESTRICTIVE)
+        ("Basic", mcrfpy.FOV.BASIC),
+        ("Diamond", mcrfpy.FOV.DIAMOND),
+        ("Shadow", mcrfpy.FOV.SHADOW),
+        ("Permissive", mcrfpy.FOV.PERMISSIVE_2),
+        ("Restrictive", mcrfpy.FOV.RESTRICTIVE)
     ]
     
     for name, algo in algorithms: