fix: follow up on linux sandbox review nits (#14440)

## Summary
- address the follow-up review nits from #13996 in a separate PR
- make the approvals test command a raw string and keep the
managed-network path using env proxy routing
- inline `--apply-seccomp-then-exec` in the Linux sandbox inner command
builder
- remove the bubblewrap-specific sandbox metric tag path and drop the
`use_legacy_landlock` shim from `sandbox_tag`/`TurnMetadataState::new`
- restore the `Feature` import that `origin/main` currently still needs
in `connectors.rs`

## Testing
- `cargo test -p codex-linux-sandbox`
- focused `codex-core` tests were rerun/started, but the final
verification pass was interrupted when I pushed at request

codex-rs/linux-sandbox/src/linux_run_main.rs

@@ -514,8 +514,8 @@ fn build_inner_seccomp_command(args: InnerSeccompCommandArgs<'_>) -> Vec<String>
         file_system_policy_json,
         "--network-sandbox-policy".to_string(),
         network_policy_json,
+        "--apply-seccomp-then-exec".to_string(),
     ];
-    inner.push("--apply-seccomp-then-exec".to_string());
     if allow_network_for_proxy {
         inner.push("--allow-network-for-proxy".to_string());
         let proxy_route_spec = proxy_route_spec