Optimize test_delete_tmp_files by using single Docker executor

Reduce test runtime by ~10s by using one DockerCommandLineCodeExecutor
instance instead of two. The delete_tmp_files=False case is covered
implicitly by other tests using the module-scoped executor fixture.

Author: Maratik555

python/packages/autogen-ext/tests/code_executors/test_docker_commandline_code_executor.py

@@ -334,19 +334,12 @@ async def test_delete_tmp_files() -> None:
         pytest.skip("Docker tests are disabled")
 
     with tempfile.TemporaryDirectory() as temp_dir:
-        # Test with delete_tmp_files=False (default)
-        async with DockerCommandLineCodeExecutor(work_dir=temp_dir) as executor:
-            cancellation_token = CancellationToken()
-            code_blocks = [CodeBlock(code="print('test output')", language="python")]
-            result = await executor.execute_code_blocks(code_blocks, cancellation_token)
-            assert result.exit_code == 0
-            assert result.code_file is not None
-            # Verify file exists after execution
-            assert Path(result.code_file).exists()
-
-        # Test with delete_tmp_files=True
+        # Test with delete_tmp_files=True using a single executor instance
+        # to avoid the overhead of creating multiple Docker containers.
         async with DockerCommandLineCodeExecutor(work_dir=temp_dir, delete_tmp_files=True) as executor:
             cancellation_token = CancellationToken()
+
+            # Test single code block
             code_blocks = [CodeBlock(code="print('test output')", language="python")]
             result = await executor.execute_code_blocks(code_blocks, cancellation_token)
             assert result.exit_code == 0