add Chinese annotations to all source files for learning purposes

Annotated 16 source files covering the full architecture:
engine (scheduler, block manager, model runner), layers (attention,
linear, sampler, etc.), model (qwen3), and utils.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nanovllm/layers/activation.py

@@ -4,6 +4,12 @@ import torch.nn.functional as F
 
 
 class SiluAndMul(nn.Module):
+    """SwiGLU 激活函数：SiLU(gate) * up。
+
+    输入是 gate 和 up 拼接的张量，沿最后一维一分为二，
+    对前半部分应用 SiLU 激活后与后半部分逐元素相乘。
+    这是 LLaMA/Qwen 系列模型中 MLP 层的标准激活函数。
+    """
 
     @torch.compile
     def forward(self, x: torch.Tensor) -> torch.Tensor: