fix: Convert big integers to float64

Large numbers can be returned by the Flexpool API reaching the `int64`
limit. Blocks reward were seen as 0 ETH. Using `float64` instead. Also
converting signed int64 to unsigned int64 for non-timestamp numbers.

BREAKING CHANGE: please follow the upgrades instructions from 1.2 to
1.3 to convert such types in the database.

Signed-off-by: Julien Riou <julien@riou.xyz>

main.go

@@ -132,7 +132,7 @@ func main() {
 				log.Warnf("Could not fetch unpaid balance: %v", err)
 				continue
 			}
-			log.Debugf("Unpaid balance %d", balance)
+			log.Debugf("Unpaid balance %.0f", balance)
 			miner.Balance = balance
 			if miner.Balance != dbMiner.Balance {
 				dbMiner.Balance = balance