fix(web): remove TYPE_CHECKING guard for AsyncTdxClient in deps.py

The typing.cast(AsyncTdxClient, ...) evaluated AsyncTdxClient at
runtime, but the import was gated behind TYPE_CHECKING, causing
NameError in production.  Direct import is safe here — web module
already depends on easy_tdx core.

src/easy_tdx/web/deps.py

@@ -2,15 +2,12 @@
 
 from __future__ import annotations
 
-import typing
-from typing import TYPE_CHECKING
-
 from fastapi import Request
 
-if TYPE_CHECKING:
-    from easy_tdx.client import AsyncTdxClient
+from easy_tdx.client import AsyncTdxClient
 
 
 def get_client(request: Request) -> AsyncTdxClient:
     """从 app.state 获取共享的 AsyncTdxClient 实例。"""
-    return typing.cast(AsyncTdxClient, request.app.state.tdx_client)
+    client: AsyncTdxClient = request.app.state.tdx_client
+    return client