Add Structured Logging for Better Observability

[cendhu]

Issue: The codebase uses unstructured logging extensively, making it difficult to parse logs programmatically.

Examples:

logger.Debugf("Batch containing %d TXs was stored in the being validated list", batchSize)
logger.Infof("Client [%d] successfully created and connected to sv at %s", i, label)

Recommendation: Adopt structured logging:

logger.Debug("batch stored for validation",
    "batch_size", batchSize,
    "service", "signature_verifier")

logger.Info("client connected",
    "client_id", i,
    "endpoint", label,
    "service", "signature_verifier")

Impact: Medium - Significantly improves log analysis and monitoring