fix(metrics): prevent unbounded growth of business_metrics

[ashnaaseth2325-oss]

Summary

business_metrics was stored in a Vec where every call to record_business_metric() kept pushing new entries with no limit or cleanup.
Over time this could cause unbounded memory growth in long-running services.

This PR replaces the vector with a bounded VecDeque and adds MAX_BUSINESS_METRICS to cap the buffer size. When the limit is reached, the oldest metric is removed before inserting a new one.

---

Steps to Reproduce

1. Run a service that records business metrics frequently.
2. Call record_business_metric() repeatedly (e.g. per request).
3. Memory usage keeps increasing because the metrics buffer never shrinks.

---

Fix

Use a bounded buffer instead of an unbounded vector.

if metrics.len() >= MAX_BUSINESS_METRICS {
    metrics.pop_front();
}
metrics.push_back(metric);

Also adds drain_business_metrics() so exporters can read and clear buffered metrics safely.

---

Verification

• Ran cargo test -p mofa-foundation --lib metrics
• Confirmed metrics are recorded correctly and buffer size stays within the defined limit.

[ashnaaseth2325-oss]

Hi @mugiwaraluffy56 @LuigiGonnella.
Kindly take a look at this PR.
Thanks!

[LuigiGonnella]

good, concise PR.

[ashnaaseth2325-oss]

Thank You!