Fixes for capnp 1.0 (#1)

* add capnp_api.h to gitignore

* Change type of read_min_bytes from size to int

Not sure why this was not causing issues before or if that
is the right fix ... but it seems to be fine :)

* Adapt python_requires to >=3.8

This was overlooked when 3.7 was deprecated. The ci no longer
works with python 3.7 and cibuildwheel uses python_requires ...

* Replace deprecated find_module with find_spec (importlib)

find_module was deprecated with python 3.4 and python 3.12
removed it (https://docs.python.org/3.12/whatsnew/3.12.html#importlib).

The new command is find_spec and only required a few adaptions

test/test_load.py

@@ -144,6 +144,7 @@ async def test_load_capnp(foo):
     baz_.text = "test"
     baz_.qux.id = 2
 
-    wrapper = foo.Wrapper._new_client(Wrapper())
-    remote = wrapper.wrapped(baz_)
-    await remote
+    async with capnp.kj_loop():
+        wrapper = foo.Wrapper._new_client(Wrapper())
+        remote = wrapper.wrapped(baz_)
+        await remote