Remove setup_request_id fallback in generated packages when google-api-core >= 2.26.0

[hebaalazzeh]

Overview

During the GAPIC request-id deduplication effort (centralizing request ID generation into google.api_core.gapic_v1.requests.setup_request_id), a backward-compatibility fallback module (_compat.py) was introduced in generated client packages to maintain compatibility with older versions of google-api-core.

Once google-api-core >= 2.26.0 (or the version containing setup_request_id) becomes the minimum required version across all generated client packages, this fallback can be removed.

Tasks

• Remove _compat.py.j2 template from gapic-generator-python.
• Update client.py.j2 and async_client.py.j2 to import setup_request_id directly from google.api_core.gapic_v1.requests.
• Remove _compat.py files from tests/integration/goldens/.