Collect metrics from plugin shell commands (#38252)

## What changed

- Provide matching local plugin commands with a sandbox-writable temporary output file through `CODEX_PLUGIN_METRICS_OUTPUT` when analytics is enabled.
- Validate successful command output against the plugin's `analytics.yaml` declaration, including measurement names, enum dimensions, finite values, duplicate rows, and size limits, before publishing analytics events.
- Keep the output path reserved from user overrides and clean up the temporary file after execution.

## Testing

- Cover output validation, limits, cleanup, sandbox permissions, environment handling, and path replacement.
- Verify measurement collection through both classic and zsh-fork shell runtimes.

GitOrigin-RevId: 88af0f87dc2f207fcbcca6af498f5c940d79349d

codex-rs/core/src/plugins/mod.rs

@@ -1,6 +1,7 @@
 mod discoverable;
 mod injection;
 mod mentions;
+pub(crate) mod metrics;
 mod render;
 #[cfg(test)]
 #[path = "skill_snapshot_tests.rs"]