FLUX.2 small decoder (#13428)

Add optional decoder_block_out_channels parameter to AutoencoderKLFlux2

Author: huemin-art

src/diffusers/models/autoencoders/autoencoder_kl_flux2.py

@@ -91,6 +91,7 @@ def __init__(
             512,
             512,
         ),
+        decoder_block_out_channels: tuple[int, ...] | None = None,
         layers_per_block: int = 2,
         act_fn: str = "silu",
         latent_channels: int = 32,
@@ -124,7 +125,7 @@ def __init__(
             in_channels=latent_channels,
             out_channels=out_channels,
             up_block_types=up_block_types,
-            block_out_channels=block_out_channels,
+            block_out_channels=decoder_block_out_channels or block_out_channels,
             layers_per_block=layers_per_block,
             norm_num_groups=norm_num_groups,
             act_fn=act_fn,