fix(metrics): reset stats on reconnect and gate metrics during warmup

- Resets all cumulative metrics (fills, cancels, inflows) and rolling stats when a new snapshot is received.
- Introduces a warmup period (200 updates) before calculating CTR/OTR to prevent abnormal initial values.
- Adds UI notifications to both the Metrics and Heatmap windows to display warmup progress.

Author: OctopusTakopi