[draft] plugin_fn extractors

[fliepeltje]

This is a proof of concept of implementing extractors based on function annotation.

This works with the Config example as described. What does not work is defining an input. For example:

@extism.plugin_fn
def count_vowels(config: extism.Config, input: str) -> Count:
  ...

will raise the following error:

Error: the `wizer.initialize` function trapped

Caused by:
    0: error while executing at wasm backtrace:
           0: 0xc3d536 - core.wasm!extism_pdk::extism::load_input::ha87e3399c3e88427
           1: 0xc3da6f - core.wasm!extism_pdk::input_bytes::hb6157a98e888d918
           2: 0x99a9 - core.wasm!core::py_module::__pyfunction_input_str::h20274f6b4ee092c8
           3: 0x8e3a - core.wasm!pyo3::impl_::trampoline::trampoline::hba91026dbca8481a
           4: 0x9984 - core.wasm!core::py_module::<impl core::py_module::input_str::MakeDef>::_PYO3_DEF::trampoline::hb47a2005df801990
           5: 0x12613f - core.wasm!cfunction_vectorcall_NOARGS
           6: 0x1da1a - core.wasm!_PyObject_VectorcallTstate
           7: 0x1f06e - core.wasm!PyObject_Vectorcall
           8: 0x2d366e - core.wasm!_PyEval_EvalFrameDefault
           9: 0x2b18db - core.wasm!_PyEval_EvalFrame
          10: 0x2b129b - core.wasm!_PyEval_Vector
          11: 0x2b0f9c - core.wasm!PyEval_EvalCode
          12: 0x36b71c - core.wasm!exec_code_in_module
          13: 0x36b40f - core.wasm!PyImport_ExecCodeModuleObject
          14: 0x36b0ab - core.wasm!PyImport_ExecCodeModuleWithPathnames
          15: 0x36b4b1 - core.wasm!PyImport_ExecCodeModuleEx
          16: 0xc4f726 - core.wasm!pyo3::types::module::PyModule::from_code_bound::hee18162d729acce4
          17: 0x19d32 - core.wasm!wizer.initialize
          18: 0xc89a3b - core.wasm!wizer.initialize.command_export
    1: Error: attempted to call an unknown imported function: 'extism:host/env' 'input_length'
       
       You cannot call arbitrary imported functions during Wizer initialization.

I'd love some help with figuring out how to not have this error :)