fix: DDIM restoration when batch_size > 1

[royale]

y_t shape is (batch_size, 3, size, size)
gamma_t and gamma_prevt shape should be (batch_size, 1, 1, 1) instead of (batch_size, 1)

failed here:

joliGEN/models/modules/diffusion_generator.py

Lines 401 to 403 in bd16f1e

	torch.sqrt(gamma_prevt)
	* (y_t - torch.sqrt(1.0 - gamma_t) * y_0_hat)
	/ torch.sqrt(gamma_t)

RuntimeError: The size of tensor a (42) must match the size of tensor b (128) at non-singleton dimension 2