Add configurable monitoring for stale Dali store with critical operator alerts

[Copilot]

Dali's main store file can go unsaved indefinitely when sasha-coalescer fails, causing unbounded delta file growth. Added monitoring to detect this condition and issue critical operator errors.

Configuration

Two new Dali attributes in dali.xsd:

• storeNotSavedWarningPeriod (default: 72 hours) - time threshold
• minDeltaSizeWarningThreshold (default: 50000 KB) - delta size threshold

Monitoring Logic

Enhanced CLightCoalesceThread to check delta file size when time threshold exceeded:

// Existing time check now also checks delta file size
if (t/3600 >= storeNotSavedWarningPeriodHours && ...) {
    StringBuffer deltaFilename(dataPath);
    iStoreHelper->getCurrentDeltaFilename(deltaFilename);
    offset_t deltaSizeKB = deltaIFile->size() / 1024;
    
    if (deltaSizeKB >= minDeltaSizeWarningThresholdKB) {
        LOG(MCoperatorError, "Store has not been saved for %u hours and delta file has grown to %llu KB...", ...);
    } else {
        OERRLOG("Store has not been saved for %u hours (delta file size: %llu KB)", ...);
    }
}

Behavior

• Both conditions met: Issues MCoperatorError with detailed diagnostic message
• Only time threshold met: Issues OERRLOG with delta size info (backward compatible)

Prevents alert fatigue while ensuring operators are notified of genuine sasha-coalescer failures before delta files consume excessive disk space.

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