Add method to download an attachment

The browser_download_url property of attachments can be confusing, as it
is a full URL and `allspice.requests_get_raw` doesn't work with absolute
URLs. The new `Attachment.download_to_file` method provides a "blessed"
way to download the attachment.

allspice/apiobject.py

@@ -1531,6 +1531,28 @@ def __eq__(self, other):
     def __hash__(self):
         return hash(self.uuid)
 
+    def download_to_file(self, io: IO):
+        """
+        Download the raw, binary data of this Attachment to a file-like object.
+
+        Example:
+
+            with open("my_file.zip", "wb") as f:
+                attachment.download_to_file(f)
+
+        :param io: The file-like object to write the data to.
+        """
+
+        response = self.allspice_client.requests.get(
+            self.browser_download_url,
+            headers=self.allspice_client.headers,
+            stream=True,
+        )
+        # 4kb chunks
+        for chunk in response.iter_content(chunk_size=4096):
+            if chunk:
+                io.write(chunk)
+
 
 class Comment(ApiObject):
     assets: List[Union[Any, Dict[str, Union[int, str]]]]

tests/test_api.py

@@ -627,6 +627,27 @@ def test_get_issue_attachments(instance):
     assert attachments[0].name == "requirements.txt"
 
 
+def test_download_issue_attachment(instance, tmp_path):
+    org = Organization.request(instance, test_org)
+    repo = Repository.request(instance, org.username, test_repo)
+    issue = repo.get_issues()[0]
+    comment = issue.get_comments()[0]
+    attachment = comment.get_attachments()[0]
+
+    filename = uuid.uuid4().hex[:8] + ".txt"
+    filepath = tmp_path / filename
+    with open(filepath, "wb") as f:
+        attachment.download_to_file(f)
+
+    with open(filepath, "r") as actual_f:
+        with open("requirements.txt", "r") as expected_f:
+            attachment_content = actual_f.read()
+            assert len(attachment_content) > 0
+
+            expected_content = expected_f.read()
+            assert expected_content == attachment_content
+
+
 def test_edit_issue_attachment(instance):
     org = Organization.request(instance, test_org)
     repo = Repository.request(instance, org.username, test_repo)