feat: use nnx.Sequential over ModuleList (#5)

Part of #1

jflux/autoencoder.py

@@ -340,16 +340,13 @@ def __init__(
         curr_res = resolution
         in_ch_mult = (1,) + tuple(ch_mult)
         self.in_ch_mult = in_ch_mult
-        # FIXME: Use nnx.Sequential instead
-        self.down = nnx.ModuleList()
         block_in = self.ch
         for i_level in range(self.num_resolutions):
-            # FIXME: Use nnx.Sequential instead
-            block = nnx.ModuleList()
+            blocks = []
             block_in = ch * in_ch_mult[i_level]
             block_out = ch * ch_mult[i_level]
             for _ in range(self.num_res_blocks):
-                block.append(
+                blocks.append(
                     ResnetBlock(
                         in_channels=block_in,
                         out_channels=block_out,
@@ -359,17 +356,17 @@ def __init__(
                     )
                 )
                 block_in = block_out
-            down = nnx.Module()
-            down.block = block
             if i_level != self.num_resolutions - 1:
-                down.downsample = Downsample(
-                    in_channels=block_in,
-                    rngs=rngs,
-                    dtype=self.dtype,
-                    param_dtype=self.param_dtype,
+                blocks.append(
+                    Downsample(
+                        in_channels=block_in,
+                        rngs=rngs,
+                        dtype=self.dtype,
+                        param_dtype=self.param_dtype,
+                    )
                 )
                 curr_res = curr_res // 2
-            self.down.append(down)
+            self.down = nnx.Sequential(*blocks)
 
         # middle
         self.middle = nnx.Sequential(
@@ -520,14 +517,12 @@ def __init__(
         )
 
         # upsampling
-        # FIXME: Use nnx.Sequential instead
         self.up = nnx.ModuleList()
         for i_level in reversed(range(self.num_resolutions)):
-            # FIXME: Use nnx.Sequential instead
-            block = nnx.ModuleList()
+            blocks = []
             block_out = ch * ch_mult[i_level]
             for _ in range(self.num_res_blocks + 1):
-                block.append(
+                blocks.append(
                     ResnetBlock(
                         in_channels=block_in,
                         out_channels=block_out,
@@ -537,17 +532,20 @@ def __init__(
                     )
                 )
                 block_in = block_out
-            up = nnx.Module()
-            up.block = block
+
+            upsample_module = [*blocks]
             if i_level != 0:
-                up.upsample = Upsample(
-                    in_channels=block_in,
-                    rngs=rngs,
-                    dtype=self.dtype,
-                    param_dtype=self.param_dtype,
+                upsample_module.append(
+                    Upsample(
+                        in_channels=block_in,
+                        rngs=rngs,
+                        dtype=self.dtype,
+                        param_dtype=self.param_dtype,
+                    )
                 )
                 curr_res = curr_res * 2
-            self.up.insert(0, up)  # prepend to get consistent order
+
+            self.up = nnx.Sequential(*upsample_module)
 
         # end
         self.norm_out = nnx.GroupNorm(