feat: include NetworkConfig through ExecParams (#11105)

This PR adds the following field to `Config`:

```rust
pub network: Option<NetworkProxy>,
```

Though for the moment, it will always be initialized as `None` (this
will be addressed in a subsequent PR).

This PR does the work to thread `network` through to `execute_exec_env()`, `process_exec_tool_call()`, and `UnifiedExecRuntime.run()` to ensure it is available whenever we span a process.

codex-rs/core/src/tasks/user_shell.rs

@@ -160,9 +160,14 @@ pub(crate) async fn execute_user_shell_command(
     });
 
     let sandbox_policy = SandboxPolicy::DangerFullAccess;
-    let exec_result = execute_exec_env(exec_env, &sandbox_policy, stdout_stream)
-        .or_cancel(&cancellation_token)
-        .await;
+    let exec_result = execute_exec_env(
+        exec_env,
+        &sandbox_policy,
+        stdout_stream,
+        turn_context.config.network.clone(),
+    )
+    .or_cancel(&cancellation_token)
+    .await;
 
     match exec_result {
         Err(CancelErr::Cancelled) => {