Following up on the [loose end from the initial
PR](https://github.com/google/bumble/pull/207#discussion_r1278015116),
we can avoid accessing the Python company id map at runtime by doing
code gen ahead of time.
Using an example to do the code gen avoids even the small build slowdown
from invoking the code gen logic in build.rs, but more importantly,
means that it's still a totally boring normal build that won't require
any IDE setup, etc, to work for everyone. Since the company ID list
changes rarely, and there's a test to ensure it always matches, this
seems like a good trade.
