Track per-worker RSS memory via Prometheus

[gagantrivedi]

Summary

Expose per-worker RSS memory as a Prometheus gauge so we can track memory growth over time in Grafana. This is essential for detecting memory leaks in production — RSS growth is often invisible to Python-level profilers, so process-level metrics are the only reliable signal.

Requirements

• Expose a Prometheus gauge metric (e.g. flagsmith_worker_rss_bytes) labelled by worker PID.
• The metric should report the RSS of the current process (e.g. via resource.getrusage or /proc/self/status).
• Updated on each request or periodically via a background thread.

Acceptance Criteria

• Prometheus metric is exported with a pid label.
• Grafana dashboard shows per-worker RSS over time.
• We can observe whether individual workers grow monotonically or stabilise.

[AAshGray]

I'm working on this