make the export work much faster

[jbinary]

functions that are wrapped into @unwrap are used very intensively and are quite slow because they use introspection at each single call. this commit improves it by a lot by introspecting the function signature at the moment of wrapping and then reusing this information to avoid evaluating it over and over again improving the performance

On my machine it reduces CPU time by almost 2x:

before:

real    0m52.974s
user    0m31.621s
sys     0m0.846s

after:

real    0m35.633s
user    0m16.681s
sys     0m0.793s