Add memory-efficient historical tracking with ring buffers

[lowhung]

Summary

Implement bounded historical tracking with smart retention for trend analysis without unbounded memory growth.

Proposed Implementation

struct RollingMetricsBuffer {
    // Ring buffer for fixed memory usage
    samples: VecDeque<MetricsSample>,
    max_samples: usize,        // e.g., 3600 for 1-hour at 1Hz
    compress_older_than: Duration,  // compress samples older than 1 hour
    
    compression_ratio: usize,  // aggregate every N old samples
}

Features

• Configurable ring buffer size (trades memory for history length)
• Automatic downsampling of old data (average every N samples)
• Memory alerts if buffer approaching limits
• Option to offload to disk for long-term storage
• Configurable retention policies

Benefits

• Predictable memory usage
• Long-term trend analysis
• No memory leaks from unbounded growth