Is it possible to lazy load the repr handlers?

When profiling my program, I find that importing cheap_repr is very expensive. Here's one profiling result using py-spy:

https://laike9m.github.io/images/af9b0d4.svg


Importing cheap_repr took ~8% of the total time. In `__init__.py`, it seems that it should be possible to make `@try_register_repr` calls lazy. Especially for registering Pandas handlers, they took most of the time. This becomes worse when users have Pandas installed but didn't really call `cheap_repr` on Pandas objects.