make things immutable to speed up dist zilla

I don't know if this might be useless because all the classes must be mutable for some reason i don't know yet, but when i ran dzil build on Moose with this patch installed, the results were massive.

Before: https://dl.dropboxusercontent.com/u/10190786/moose_nytprof.zip

After: https://dl.dropboxusercontent.com/u/10190786/moose_nytprof_2.zip