fix(arch_diagram): 生成器自写尾换行（gen_net_pending/gen_memory）

gen_*.py 里 8 个已自带尾换行（'...</svg>\n'），仅
gen_net_pending_svg.py 少一个尾 \n → 每次重跑都被 pre-commit 的
end-of-file-fixer 补回，产生无意义的 1 行尾差异。

- gen_net_pending_svg.py: return "\n".join(svg) + "\n"，
  并把 open(...) 补 newline="\n"（与其余生成器一致）
- gen_memory_svg.py: open(...) 补 newline="\n"（输出本已带尾换行）

重跑验证：Net层阻塞模型.svg 与已提交 blob 逐字节一致
（hash-object --path 相同、git diff 为空）；内存 3 张 SVG 亦无差异。

tools/arch_diagram/gen_memory_svg.py

@@ -365,7 +365,7 @@ def main():
     for filename, gen_func in targets:
         path = os.path.join(out_dir, filename)
         svg = gen_func()
-        with open(path, "w", encoding="utf-8") as f:
+        with open(path, "w", encoding="utf-8", newline="\n") as f:
             f.write(svg)
         print(f"OK: {filename} ({len(svg)} bytes)")
 

tools/arch_diagram/gen_net_pending_svg.py

@@ -284,13 +284,13 @@ def build():
            'viewBox="0 0 %d %d" font-family="%s">' % (W, H, W, H, FONT)]
     svg.extend(out)
     svg.append('</svg>')
-    return "\n".join(svg)
+    return "\n".join(svg) + "\n"
 
 
 def main():
     svg = build()
     os.makedirs(os.path.dirname(OUT), exist_ok=True)
-    with open(OUT, "w", encoding="utf-8") as f:
+    with open(OUT, "w", encoding="utf-8", newline="\n") as f:
         f.write(svg)
     print("已生成: %s (%d bytes)" % (OUT, len(svg.encode("utf-8"))))