Validation utilities

Validation utilities

Shared helpers in torml.utils (all torch-backed):

• check_array — dtype (torch.dtype or "float32" string), ensure_2d, allow_nd, copy, force_all_finite, min samples/features, device preservation.
• check_X_y — paired validation with equal-length enforcement.
• check_is_fitted — raises NotFittedError (a ValueError) when fitted attributes (coef_, intercept_, labels_, classes_) are missing.
• check_random_state — None / int / torch.Generator → generator.
• check_scalar — type + bounds checking for hyperparameters.