ci: add import profiler check across monorepo

[hebaalazzeh]

Overview

This PR integrates the import profiler script (introduced in #17467) into our automated CI pipeline.

Why this matters: Import times significantly impact CLI responsiveness and cold starts for Serverless products like Cloud Run and Cloud Functions. Ideally, library imports should stay under 500ms, and anything taking over 1 second is a target for optimization. This CI check helps us proactively track metrics like import latency, memory footprint, and code volume to prevent performance regressions on critical libraries (e.g., aiplatform).

Changes Included

• GitHub Actions Workflow: Created a new workflow (.github/workflows/import-profiler.yml) that triggers on PRs and merge groups. The workflow is pinned specifically to Python 3.15.
• Native CI Script Integration: Instead of injecting a new session into the 400+ noxfile.py configs, the profiling logic is embedded directly in ci/run_single_test.sh. The script dynamically extracts the valid module name from setup.py and passes it to the profiler.
• Conditional Execution: Integrated with ci/run_conditional_tests.sh so that the import_profile check is only executed against packages that have been modified in the current pull request.

Related PRs

• Builds upon the import profiler tool added in feat: add import profiler tool with dynamic loaded lines code volume … feat: add import profiler tool with dynamic loaded lines code volume … #17467

[gemini-code-assist]

Code Review

This pull request adds a new import_profile session to the noxfile.py.j2 template to measure and ensure import times remain below defined thresholds. Feedback points out that because this template is used in standalone repositories outside of the monorepo, referencing a relative path to the monorepo's root scripts directory will cause default nox runs to fail in those environments. It is recommended to check for the script's existence and gracefully skip the session if it is missing, while also using pathlib.Path for cleaner path handling.