bucketpool: do not use floating point math
bucketpool: do not use floating point math

name        old time/op  new time/op  delta
Pool-16      281ns ± 1%   244ns ± 2%  -13.15%  (p=0.000 n=10+10)

Signed-off-by: Vicent Marti <2a2c16577cf04fb953d196f935e266724d4c66a1@strn.cat>

tinyspeck/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,mahak/vitess,tinyspeck/vitess,mahak/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,tinyspeck/vitess,tinyspeck/vitess