Related to #801

Whenever we load a plugin, if we see that the module imports missing or mismatching items from extism:host/env, we can:

1. Emit a warning logline advising the user to install a newer version of the host sdk.
2. Stub the import with a failing host function.

Dynamic pdks (like js-pdk) would still be "backwards" compatible so long as newer host functionality isn't used.