fix: #102 update to guarantee thread-safe when handling failed pool offline data

[Sotatek-HuyLe3a]

#102
This error occurs in: (PoolOfflineDataStoringServiceImpl.java)

 poolDataMap.entrySet().parallelStream().forEach(poolDataEntry -> {
            Long poolId = poolDataEntry.getKey();
            PoolData poolData = poolDataEntry.getValue();
            PoolHash poolHash = poolHashMap.get(poolId);
            PoolMetadataRef poolMetadataRef = poolMetadataRefMap.get(poolData.getMetadataRefId());
            // if pool offline data exist then update
            PoolOfflineFetchError poolOfflineFetchError = poolOfflineFetchErrorRepository
                    .findByPoolHashAndPoolMetadataRef(poolHash, poolMetadataRef);

            // if pool offline fetch error exist then update
            if (!Objects.isNull(poolOfflineFetchError)) {
                poolOfflineFetchError.setFetchTime(Timestamp.valueOf(LocalDateTime.now(ZoneOffset.UTC)));
                poolOfflineFetchError.setRetryCount(poolOfflineFetchError.getRetryCount() + 1);
                poolOfflineFetchError.setFetchError(poolData.getErrorMessage());
            } else {
                poolOfflineFetchError = PoolOfflineFetchError.builder()
                        .poolHash(poolHash)
                        .poolMetadataRef(poolMetadataRef)
                        .fetchError(poolData.getErrorMessage())
                        .retryCount(BigInteger.ONE.intValue())
                        .fetchTime(Timestamp.valueOf(LocalDateTime.now(ZoneOffset.UTC)))
                        .build();
            }
            poolOfflineFetchErrorsNeedSave.add(poolOfflineFetchError);
        });

It's not thread safe when using parallel stream with forEach, and add elements into a ArrayList.
Solution: use Stream map() function and Collector interface instead.