feat: api command should list attributes of classes (#1112)

Closes #1107.

### Summary of Changes

added an attribute ´instance_attribute´ to the class 'class'.

### Testing Instructions

run `package-parser api -p sklearn -o ./out` and compare the output with
the original file that the class contains.
`package-parser annotations -a ../data/api/sklearn__api.json -u
../data/usages/sklearn_usages_counts.json -o ./out/annotations.json` can
verify that no error occur if the file is loaded.

Co-authored-by: Lars Reimann <[email protected]>

Author: Aclrian

package-parser/package_parser/processing/api/_ast_visitor.py

@@ -133,6 +133,7 @@ def leave_module(self, _: astroid.Module) -> None:
 
     def enter_classdef(self, class_node: astroid.ClassDef) -> None:
         qname = class_node.qname()
+        instance_attributes = list(class_node.instance_attrs)
 
         decorators: Optional[astroid.Decorators] = class_node.decorators
         if decorators is not None:
@@ -149,6 +150,7 @@ def enter_classdef(self, class_node: astroid.ClassDef) -> None:
             is_public=self.is_public(class_node.name, qname),
             reexported_by=self.reexported.get(qname, []),
             documentation=self.documentation_parser.get_class_documentation(class_node),
+            instance_attributes=instance_attributes,
         )
         self.__declaration_stack.append(class_)
 

package-parser/package_parser/processing/api/model/_api.py

@@ -206,6 +206,7 @@ def from_json(json: Any) -> Class:
                 description=json.get("description", ""),
                 full_docstring=json.get("docstring", ""),
             ),
+            json.get("instance_attributes", []),
         )
 
         for method_id in json["methods"]:
@@ -222,6 +223,7 @@ def __init__(
         is_public: bool,
         reexported_by: list[str],
         documentation: ClassDocumentation,
+        instance_attributes: list[str],
     ) -> None:
         self.id: str = id_
         self.qname: str = qname
@@ -231,6 +233,7 @@ def __init__(
         self.is_public: bool = is_public
         self.reexported_by: list[str] = reexported_by
         self.documentation: ClassDocumentation = documentation
+        self.instance_attributes = instance_attributes
 
     @property
     def name(self) -> str:
@@ -251,6 +254,7 @@ def to_json(self) -> Any:
             "reexported_by": self.reexported_by,
             "description": self.documentation.description,
             "docstring": self.documentation.full_docstring,
+            "instance_attributes": self.instance_attributes,
         }