Help wanted: add size-limit check in CI

[drwpow]

openapi-fetch as it’s grown in features has grown in size! It was originally 2 kb when it started out, but with middleware support and other features is now closer to 6 kb (technically 5.8 kb but who’s counting?—wait we need to!).

Adding something like Size Limit (or something else) in CI to make sure the bundle size doesn’t increase would be helpful. The goal of this check isn’t to prevent any features or bugfixes if they add to the weight at all, rather, it just helps prevent unintentional size increases. We can always decide to increase the package weight if it provides value for the weight.