Fix test issues and optimize test execution

- Fixed 'TestOpponent' import error in 'test_sequence_player.py'.
- Refactored test classes with '__init__' constructors to avoid PytestCollectionWarning.
- Addressed UserWarnings in 'test_memoryone.py' and 'test_memorytwo.py' related to default player settings.
- Handled seed reproducibility warning in 'test_player.py' to ensure deterministic test results.
- Investigated RuntimeWarning in 'test_zero_determinant.py' related to invalid division.
- Optimized test execution time by running tests in parallel using pytest-xdist.
- Addressed minor warnings related to test strategies and examples.

Author: Mike014

axelrod/tests/strategies/test_sequence_player.py

@@ -6,7 +6,7 @@
 from axelrod._strategy_utils import recursive_thue_morse
 from axelrod.strategies.sequence_player import SequencePlayer
 
-from .test_player import TestOpponent, TestPlayer
+from .test_player import OpponentTest, TestPlayer
 
 C, D = axl.Action.C, axl.Action.D
 
@@ -26,7 +26,7 @@ def cooperate_gen():
             yield 1
 
         player = SequencePlayer(generator_function=cooperate_gen)
-        opponent = TestOpponent()
+        opponent = OpponentTest()
         self.assertEqual(C, player.strategy(opponent))