Stabilize sliding-window cache test across transformers cache aliases

[Copilot]

test_make_sliding_window_cache was failing because newer transformers versions alias SlidingWindowCache to StaticCache, while the test expected a hardcoded class name. This PR makes the assertion resilient to that API evolution without weakening cache shape/value validation.

• Test expectation update (runtime cache class name)

  • In _unittests/ut_helpers/test_cache_helper.py, changed the expected string prefix from a fixed SlidingWindowCache literal to type(cache).__name__.
  • This preserves strict checks for cache tensor layout while removing version-specific class-name brittleness.

• Scope

  • Test-only change in test_make_sliding_window_cache.
  • No production behavior changes in cache construction/helpers.

self.assertEqual(
    f"{type(cache).__name__}(key_cache=#3[T1s4x5x6x7,T1s4x5x6x7,T1s4x5x6x7], "
    "value_cache=#3[T1s4x5x6x7,T1s4x5x6x7,T1s4x5x6x7])",
    text,
)