FIX Handle lazy import failures during trusted type discovery in skops.io

[Copilot]

Importing transformers before skops.io could raise ModuleNotFoundError when transformers lazy attributes attempted to import optional vision dependencies (e.g. torchvision) during skops trusted-type enumeration. This PR makes module discovery tolerant of those lazy import failures.

• Root-cause containment in module resolution

  • Updated skops/io/_utils.py::whichmodule to ignore ImportError in addition to AttributeError while scanning sys.modules.
  • This prevents optional-dependency import failures from aborting skops.io import-time trusted-type collection.

• Regression coverage for lazy-module behavior

  • Added a focused test in skops/io/tests/test_utils.py that injects a lazy module into sys.modules whose __getattr__ raises ModuleNotFoundError.
  • Verifies whichmodule(...) safely falls back instead of propagating the error.

• Behavioral change (minimal and targeted)

# before
except AttributeError:
    pass

# after
except (AttributeError, ImportError):
    pass

• Fixes bug: import transformer before skops causes ModuleNotFoundError #527