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/core/src/tools/registry.rs

@@ -173,7 +173,6 @@ impl ToolRegistry {
                 sandbox_tag(
                     &invocation.turn.sandbox_policy,
                     invocation.turn.windows_sandbox_level,
-                    invocation.turn.features.use_legacy_landlock(),
                 ),
             ),
             (
@@ -498,12 +497,8 @@ async fn dispatch_after_tool_use_hook(
                     success: dispatch.success,
                     duration_ms: u64::try_from(dispatch.duration.as_millis()).unwrap_or(u64::MAX),
                     mutating: dispatch.mutating,
-                    sandbox: sandbox_tag(
-                        &turn.sandbox_policy,
-                        turn.windows_sandbox_level,
-                        turn.features.use_legacy_landlock(),
-                    )
-                    .to_string(),
+                    sandbox: sandbox_tag(&turn.sandbox_policy, turn.windows_sandbox_level)
+                        .to_string(),
                     sandbox_policy: sandbox_policy_tag(&turn.sandbox_policy).to_string(),
                     output_preview: dispatch.output_preview.clone(),
                 },