fix: Default AsyncPredictor upload prefix to endpoint name

[lucasjia-aws]

Issue

Fixes #3210
Fixes #4774

V3 counterpart: #6336

Problem

sagemaker.predictor_async.AsyncPredictor(predictor) defaults name to None, but calling predict(data=...) or predict_async(data=...) without an input_path fails with TypeError: 'NoneType' object is not subscriptable. This was reported on 2.92.1 (#3210) and again on 2.224.2 (#4774).

Root cause

AsyncPredictor._upload_data_to_s3 builds the S3 key with name_from_base(self.name, short=True), and name_from_base slices its base argument without a None guard. The existing unit test test_async_predict_call_with_data only passed because it set predictor_async.name manually before calling predict_async.

Fix

• In _upload_data_to_s3, use self.name or self.endpoint_name as the base for the S3 key prefix. An explicitly provided name is still used unchanged, and self.name is not modified.
• Documented the name argument in the AsyncPredictor.__init__ docstring.

Testing

• Added test_async_predict_call_with_data_and_no_name and test_async_predict_call_with_data_and_name_uses_name in tests/unit/test_predictor_async.py, using a real Predictor with a mocked session.
• The no-name regression test fails on the current master-v2 and passes with this change; tests/unit/test_predictor_async.py passes 22/22.
• flake8 passes on the changed files.