name                 old time/op    new time/op    delta
unzlib/py/wczdata      20.8µs ± 2%    20.7µs ± 1%     ~     (p=0.421 n=5+5)
unzlib/go/wczdata      64.4µs ± 1%    21.3µs ± 0%  -66.89%  (p=0.008 n=5+5)
unzlib/py/prod1-avg    4.00µs ± 1%    4.02µs ± 1%     ~     (p=0.421 n=5+5)
unzlib/go/prod1-avg    10.4µs ± 1%     4.3µs ± 1%  -58.72%  (p=0.008 n=5+5)

There is also unsafe interface with czlib.UnsafeDecompress & friends which I
had not tried because even using safe interface brings ~ 3x speedup.