Run pyright as part of @tb.typecheck, batch all typechecks (#889)

pyright doesn't have a cache, so I didn't want to rerun pyright fully
for every test.  So instead I have us generate one file per test case
as part of test suite setup, typecheck all the files at once, and then
check the messages for each file in the individual tests.

This speeds things up for mypy too quite a bit, because loading all
the caches is actually pretty expensive too.

Fixes #878.

@elprans Two tests didn't work for reasons involving splats in shapes.