specify to package the protobuf snapshot

the REUSE stuff made simple discovery not work, so setuptools had to be
corrected, this has probably been wrong since then

pyproject.toml

@@ -75,7 +75,10 @@ ignore_errors = true
 python_files = ["*_tests.py", "tests.py", "test_*.py"]
 
 [tool.setuptools]
-packages = ["gp2040ce_bintools"]
+packages = [
+    "gp2040ce_bintools",
+    "gp2040ce_bintools.proto_snapshot",
+]
 
 [tool.setuptools_scm]
 write_to = "gp2040ce_bintools/_version.py"