[perf] Parallel builds

[sneakers-the-rat]

not much of a perf gain, but it's something - build schemas within a namespace in parallel with multiprocessing. goes from 1:55s down to 1:17s.

We also finally were forced to delete some monkeypatches because they break pickling, which fixed our import ordering because of the fixes i made on upstream schemaview import ordering.

not sure why attributes are a list instead of a dict now, but i also don't mind it.

[coveralls]

coverage: 73.854% (+0.1%) from 73.732%
when pulling a604990 on perf-generator
into 98a9975 on main.