add typechecking of docs/examples to ci

[nclack]

In #171, there was a problem with type-checking exposed when a user tried to use the documented examples. This got fixed in #173 but exposed a testing gap.

We type-check in CI, but this doesn't test whether the types get exposed correctly. That should get fixed.

[tlambert03]

I was also gonna suggest perhaps extracting the code blocks and executing them as well. I ran into some issues running through the docs with new chunking apis.

I'll see if I can do that in a PR :)