[execution-layer] - Add structured logging with request tracing

[Txrmarcos]

eplace all console.log/warn/error with structured logger (Pino — already used in database service). Add per-request traceId (UUID) injected via middleware. Log format: { traceId, chain, protocol, method, durationMs, rpcEndpoint, status }. Tag logs with chain + protocol. Log which RPC endpoint was used per request. Files: new backend/src/shared/logger.ts, backend/src/middleware/tracing.ts, update all usecases.