optimize tsm1.FloatDecoder
optimize tsm1.FloatDecoder

This commit changes the `FloatDecoder.val` from a `float64` type
to a `uint64` to avoid an additional type conversion during read.
Now the type gets converted to a `float64` only on call to `Values()`.

chenziliang/influxdb,influxdb/influxdb,linearb/influxdb,pkittenis/influxdb,runner-mei/influxdb,daachi/influxdb,arussellsaw/influxdb,apigee/influxdb,arussellsaw/influxdb,jgeiger/influxdb,chenziliang/influxdb,apigee/influxdb,mnuessler/influxdb,archsaber/influxdb,apigee/influxdb,jgeiger/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,jipperinbham/influxdb,mvadu/influxdb,arussellsaw/influxdb,vladlopes/influxdb,archsaber/influxdb,archsaber/influxdb,chenziliang/influxdb,pkittenis/influxdb,otoolep/influxdb,mark-rushakoff/influxdb,mvadu/influxdb,mnuessler/influxdb,jipperinbham/influxdb,pkittenis/influxdb,daachi/influxdb,linearb/influxdb,influxdb/influxdb,joaopedrotaveira/influxdb,arussellsaw/influxdb,mark-rushakoff/influxdb,jgeiger/influxdb,joaopedrotaveira/influxdb,mark-rushakoff/influxdb,joaopedrotaveira/influxdb,mvadu/influxdb,influxdb/influxdb,jgeiger/influxdb,mark-rushakoff/influxdb,li-ang/influxdb,archsaber/influxdb,otoolep/influxdb,influxdb/influxdb,apigee/influxdb,pkittenis/influxdb,vladlopes/influxdb,benbjohnson/influxdb,jipperinbham/influxdb,joaopedrotaveira/influxdb,daachi/influxdb,influxdb/influxdb,runner-mei/influxdb,jipperinbham/influxdb,runner-mei/influxdb,linearb/influxdb,daachi/influxdb,mvadu/influxdb,runner-mei/influxdb,mvadu/influxdb,nooproblem/influxdb,mvadu/influxdb,daachi/influxdb,arussellsaw/influxdb,otoolep/influxdb,vladlopes/influxdb,joaopedrotaveira/influxdb,influxdata/influxdb,benbjohnson/influxdb,apigee/influxdb,pkittenis/influxdb,otoolep/influxdb,mark-rushakoff/influxdb,linearb/influxdb,influxdata/influxdb,mnuessler/influxdb,mnuessler/influxdb,jgeiger/influxdb,jgeiger/influxdb,nooproblem/influxdb,vladlopes/influxdb,daachi/influxdb,li-ang/influxdb,nooproblem/influxdb,benbjohnson/influxdb,otoolep/influxdb,otoolep/influxdb,apigee/influxdb,pkittenis/influxdb,jipperinbham/influxdb,linearb/influxdb,mnuessler/influxdb,nooproblem/influxdb,jipperinbham/influxdb,nooproblem/influxdb,benbjohnson/influxdb,chenziliang/influxdb,mnuessler/influxdb,arussellsaw/influxdb