Tweak to model invalidation and test for buffer caches being cleared

Author: jonathanhogg

src/flitter/render/window/models.pyx

@@ -146,6 +146,7 @@ cdef class Model:
             for cache in self.buffer_caches:
                 if self.name in cache:
                     del cache[self.name]
+            self.buffer_caches = None
 
     cpdef object get_trimesh(self):
         self.cache_timestamp = perf_counter()

tests/test_models.py

@@ -509,3 +509,5 @@ def test_box_get_buffers(self):
         index_data = glctx.buffer.mock_calls[1].args[0]
         self.assertEqual(index_data.dtype.name, 'int32')
         self.assertEqual(index_data.shape, (12, 3))
+        model.invalidate()
+        self.assertNotIn(model.name, objects)