feat: 新增LoRA微调模块

- LoRALinear基于register_parameter托管base weight，state_dict路径不变
- inject_lora/merge_lora/save_lora/load_lora完备封装
- 24个单元测试覆盖注入、合并、存取、边界场景

astrai/model/__init__.py

@@ -2,6 +2,13 @@ from astrai.model.automodel import AutoModel
 from astrai.model.components.attention import GQA
 from astrai.model.components.decoder_block import DecoderBlock
 from astrai.model.components.linear import Linear
+from astrai.model.components.lora import (
+    LoRAConfig,
+    inject_lora,
+    load_lora,
+    merge_lora,
+    save_lora,
+)
 from astrai.model.components.mlp import MLP
 from astrai.model.components.norm import RMSNorm
 from astrai.model.encoder import EmbeddingEncoder
@@ -18,4 +25,10 @@ __all__ = [
     "AutoRegressiveLM",
     "EmbeddingEncoder",
     "AutoModel",
+    # LoRA
+    "LoRAConfig",
+    "inject_lora",
+    "merge_lora",
+    "save_lora",
+    "load_lora",
 ]