replace deprecated paddle compat torch proxy alias

[ShigureNyako]

📌 Description

• 将仓库中的 paddle.compat.enable_torch_proxy 旧别名替换为公开 API paddle.enable_compat
• 覆盖 README 用法示例、3 个测试文件中的实际调用，以及 1 处测试注释中的旧写法
• 仅做 compat API 名称替换，不改动测试逻辑

🔍 Related Issues

• 无
• 背景：paddle.compat.enable_torch_proxy 是早期开发别名，后续将移除

🚀 Pull Request Checklist

• I have installed pre-commit by running pip install pre-commit (or used your preferred method).
• I have installed the hooks with pre-commit install.
• I have run the hooks manually with pre-commit run --all-files and fixed any reported issues.

🧪 Tests

• Tests have been added or updated as needed.
• rg -n -F "paddle.compat.enable_torch_proxy" . 返回 0 命中
• python3 -m py_compile tests/moe/test_trtllm_gen_fused_moe.py tests/conftest.py tests/attention/test_attention_sink_blackwell.py tests/comm/test_trtllm_allreduce_fusion_paddle.py 通过
• Full test suite not run in this environment.

Reviewer Notes

• 这是 compat API 公开化后的最小替换，便于后续移除旧别名

[ShigureNyako]

自查完成：

• README 与 3 个测试文件中的 paddle.compat.enable_torch_proxy 已替换为 paddle.enable_compat
• 1 处测试注释中的旧写法也已同步更新
• rg -n -F "paddle.compat.enable_torch_proxy" . 返回 0 命中
• python3 -m py_compile tests/moe/test_trtllm_gen_fused_moe.py tests/conftest.py tests/attention/test_attention_sink_blackwell.py tests/comm/test_trtllm_allreduce_fusion_paddle.py 已通过

@SigureMo 请审阅，感谢。

[SigureMo]

duplicate with #11