fix: wire FrameworkProcessor code_location into code upload paths

[humanzz]

FrameworkProcessor.__init__ accepts code_location and the docstring states it controls where code is uploaded, but _package_code and _create_and_upload_runproc always used default_bucket(), ignoring it (Bug 2 reported in #5765)

• Add _s3_code_prefix() helper that returns code_location when set, falling back to default_bucket()/default_bucket_prefix
• Use _s3_code_prefix() in _package_code for sourcedir.tar.gz upload
• Use _s3_code_prefix() in _create_and_upload_runproc pipeline path for runproc.sh upload
• Non-pipeline runproc.sh and _patch_inputs_with_payload already derive their URIs from _package_code's output, so they inherit the fix

Issue #, if available:

#5765 (Bug 2)

Problem

processor = FrameworkProcessor(
    ...,
    code_location="s3://my-custom-bucket",  # ← accepted but ignored
)
processor.run(code="my_script.py", source_dir="src", wait=False)
# Code uploads to s3://sagemaker-us-west-2-123456789/... instead of s3://my-custom-bucket/...

Fix

A single _s3_code_prefix() method that all code upload paths use:

def _s3_code_prefix(self):
    if self.code_location:
        return self.code_location
    return s3.s3_path_join(
        "s3://", self.sagemaker_session.default_bucket(),
        self.sagemaker_session.default_bucket_prefix or "",
    )

All S3 URIs for code artifacts (sourcedir.tar.gz, runproc.sh, pipeline-hashed paths) now flow through this method.

Changes

File	Change
sagemaker-core/.../processing.py	Add _s3_code_prefix(), use it in _package_code and _create_and_upload_runproc
sagemaker-core/tests/unit/test_processing.py	3 new tests: custom code_location, default bucket fallback, trailing slash handling

Testing

• 83 processing unit tests pass (80 existing + 3 new)
• New tests verify:
  • code_location="s3://my-custom-bucket/my-prefix" → upload URI starts with that prefix
  • No code_location → upload URI uses mock session's default_bucket (test-bucket/sagemaker)
  • code_location="s3://bucket/" (trailing slash) → stripped by __init__, works correctly

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