Add Mistral3 multimodal support with Pixtral vision encoder

This adds support for Mistral3 multimodal models (vision + text):

- `Bumblebee.Vision.Pixtral`: Pixtral vision encoder with RoPE support
- `Bumblebee.Text.Mistral3`: Mistral3 text decoder with interleaved attention
- `Bumblebee.Multimodal.Mistral3`: Vision-language model combining Pixtral
  and Mistral3 with multimodal projector for image-conditioned generation
- Ministral/Ministral3 variant support with interleaved attention
- Devstral 2 (Ministral3) model support

Supported architectures:
- PixtralVisionModel
- Mistral3Model, Mistral3ForCausalLM, Mistral3ForSequenceClassification
- Mistral3ForConditionalGeneration (multimodal)
- Ministral3ForCausalLM

Author: dai-yamashita

lib/bumblebee.ex

@@ -170,6 +170,13 @@ defmodule Bumblebee do
     "MistralModel" => {Bumblebee.Text.Mistral, :base},
     "MistralForCausalLM" => {Bumblebee.Text.Mistral, :for_causal_language_modeling},
     "MistralForSequenceClassification" => {Bumblebee.Text.Mistral, :for_sequence_classification},
+    "Mistral3Model" => {Bumblebee.Text.Mistral3, :base},
+    "Mistral3ForCausalLM" => {Bumblebee.Text.Mistral3, :for_causal_language_modeling},
+    "Mistral3ForSequenceClassification" =>
+      {Bumblebee.Text.Mistral3, :for_sequence_classification},
+    "Ministral3ForCausalLM" => {Bumblebee.Text.Mistral3, :for_causal_language_modeling},
+    "Mistral3ForConditionalGeneration" =>
+      {Bumblebee.Multimodal.Mistral3, :for_conditional_generation},
     "PhiModel" => {Bumblebee.Text.Phi, :base},
     "PhiForCausalLM" => {Bumblebee.Text.Phi, :for_causal_language_modeling},
     "PhiForSequenceClassification" => {Bumblebee.Text.Phi, :for_sequence_classification},
@@ -198,6 +205,7 @@ defmodule Bumblebee do
     "T5Model" => {Bumblebee.Text.T5, :base},
     "T5ForConditionalGeneration" => {Bumblebee.Text.T5, :for_conditional_generation},
     "T5EncoderModel" => {Bumblebee.Text.T5, :encoder},
+    "PixtralVisionModel" => {Bumblebee.Vision.Pixtral, :base},
     "ViTForImageClassification" => {Bumblebee.Vision.Vit, :for_image_classification},
     "ViTForMaskedImageModeling" => {Bumblebee.Vision.Vit, :for_masked_image_modeling},
     "ViTModel" => {Bumblebee.Vision.Vit, :base},
@@ -255,6 +263,8 @@ defmodule Bumblebee do
     "layoutlm" => :layout_lm,
     "llama" => :llama,
     "mistral" => :llama,
+    "mistral3" => :llama,
+    "ministral3" => :llama,
     "mbart" => :mbart,
     "phi" => :code_gen,
     "phi3" => :llama,

lib/bumblebee/layers/transformer.ex

@@ -25,6 +25,12 @@ defmodule Bumblebee.Layers.Transformer do
       - a keyword list (applied to all blocks)
       - a function that takes the block index and returns the configuration
 
+    * `:attention_window_size` - window size for sliding attention. Can be:
+      - a tuple `{left_size, right_size}` (applied to all blocks)
+      - a function that takes the block index and returns the configuration
+        (useful for interleaved attention patterns)
+      - `nil` for global attention
+
     * `:name` - the prefix for layer names
 
   For all other options (including required options) see `block/2`.
@@ -52,7 +58,6 @@ defmodule Bumblebee.Layers.Transformer do
       :output_use_bias,
       :layer_norm,
       :block_type,
-      :attention_window_size,
       :scale_attention_weights
     ]
 
@@ -64,6 +69,7 @@ defmodule Bumblebee.Layers.Transformer do
             :name,
             :num_blocks,
             :rotary_embedding,
+            :attention_window_size,
             attention_mask: Layers.none(),
             attention_head_mask: Layers.none(),
             attention_relative_bias: nil,
@@ -85,6 +91,7 @@ defmodule Bumblebee.Layers.Transformer do
     cross_attention_head_mask = opts[:cross_attention_head_mask]
     cache = opts[:cache]
     rotary_embedding = opts[:rotary_embedding]
+    attention_window_size = opts[:attention_window_size]
 
     block_opts = Keyword.take(opts, block_opts_keys)
 
@@ -121,6 +128,13 @@ defmodule Bumblebee.Layers.Transformer do
               config when is_list(config) -> config
             end
 
+          block_attention_window_size =
+            case attention_window_size do
+              nil -> nil
+              fun when is_function(fun, 1) -> fun.(idx)
+              config -> config
+            end
+
           {hidden_state, attention, cross_attention, block_cache, attention_relative_bias} =
             block(
               state.hidden_state,
@@ -134,6 +148,7 @@ defmodule Bumblebee.Layers.Transformer do
                 block_cache: block_cache,
                 offset: offset,
                 rotary_embedding: block_rotary_embedding,
+                attention_window_size: block_attention_window_size,
                 name: join(name, idx)
               ] ++ block_opts
             )