chore: apply linting fixes and expand ruff coverage to test suite

tests/test_frame_player.py

@@ -1,30 +1,31 @@
 from pygui.backend.models.frame import Frame
 from pygui.backend.models.frame_player import FramePlayer
 
+
 def frames(n):
     return [Frame(seq=i, time=float(i), values=[149.0 + i])for i in range(n)]
 
 def test_loads_and_reports_total():
     p = FramePlayer(); p.load(frames(3))
-    assert p.total == 3 and p.index == 0 
+    assert p.total == 3 and p.index == 0
     current = p.current()
     assert current is not None
     assert current.values == [149.0]
-    
+
 def test_step_forward_and_back_clamps():
     p = FramePlayer(); p.load(frames(3))
     assert p.step(1).index == 1
     assert p.step(1).index == 2
     assert p.step(1).index == 2
     assert p.step(-5).index == 0
-    
+
 def test_seek():
     p = FramePlayer(); p.load(frames(5))
     assert p.seek(3).index == 3
     assert p.seek(99).index == 4
-    
+
 def test_at_end():
     p = FramePlayer(); p.load(frames(2))
     assert not p.at_end
     p.seek(1)
-    assert p.at_end
+    assert p.at_end