refactor : 将 config 对象直接传给 DecoderBlock，替代 16 个独立参数

- DecoderBlock.__init__ 改为 (config, layer_id)，内部用 asdict
  展开字段给 AttnFactory/FFNFactory，factory 按 __init__ 签名自动过滤
- EncoderConfig 补充 attn_type 和 ffn_type 字段
- 314 个测试全部通过

astrai/config/model_config.py

@@ -70,10 +70,12 @@ class EncoderConfig(BaseModelConfig):
     rope_theta: Optional[float] = None
     rope_scaling: Optional[dict] = None
 
+    attn_type: str = "gqa"
     n_heads: Optional[int] = None
     n_kv_heads: Optional[int] = None
     use_qk_norm: Optional[bool] = None
     use_gated_attention: Optional[bool] = None
 
+    ffn_type: str = "mlp"
     pooling_type: Optional[str] = None
     normalize_embeddings: Optional[bool] = None