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

setup.py

@@ -210,7 +210,7 @@ extensions = [
 ]
 
 setup(
-    python_requires=">=3.7",
+    python_requires=">=3.8",
     name="pycapnp",
     packages=["capnp"],
     version=VERSION,