The `Makefile` and `make.bat` are autogenerated via `sphinx-quickstart`;
generally we'll want to use `just docs` instead. I left them in in case
they're load-bearing for readthedocs (which we'll want to enable when we
make this repo public.)

Infer host function Wasm types from type annotations if given. When
inferred, parameters and return values are automatically marshaled and
unmarshaled and "current plugin" access is hidden. Whenever a host
function is declared, add it to a thread-local registry of host
functions. Default `Plugin` creation will use the global list of
plugins.

In the weeds note: because this means we have to hang on to functions at
specific addresses, we always end up using user_data now: in particular
we store the offset of the target host function in the user_data to
determine which implementation to call. I added this because the FFI
call would fail if the target python host function wasn't available at
module-level; this would turn into a stack overflow (it appeared that
the runtime tried to re-invoke a host function infinitely if it couldn't
find it.)

---

Example of inferred decorator + global host func registry:

```python
import typings
import extism
@extism.host_fn()
def incr_json(input: typings.Annotated[dict, extism.Json]) -> str
    return input.get("hello", "world")

with extism.Plugin(some_wasm_file) as plugin:
    plugin.call("incr_json", json.dumps({"hello", "earth"}))
```