feat(google-backstory): new library google-backstory

[suztomo]

I manually edit librarian.yaml and librarian.state file and ran $ docker run -u $(id -u):$(id -g) -v .:/repo -v ~/.cache:/.cache -w /repo docker.io/library/librarian-python:${V} generate -v google-backstory.

I referenced the google-cloud-common declaration in librarian.yaml. At first, I hit 2026/06/04 14:33:45 librarian: generate library "google-backstory" (python): error creating metadata for google-backstory: default version must be specified for every library with generated APIs error but this was resolved by declaring default_version: apiVersion.

Unit Test Failure and Fix

The CI check failed because google-backstory is a type-only library and had no unit tests, causing pytest to exit with code 5 (no tests collected).

To fix this, I added:

• test_packaging.py to verify namespace package compatibility.
• test_backstory.py to verify that backstory types can be imported.

This follows the pattern of google-cloud-common which also has a dummy test to avoid empty test suite failures. I also updated librarian.yaml (keep) and .librarian/state.yaml (preserve_regex) to preserve these tests during regeneration.

[gemini-code-assist]

Code Review

This pull request introduces the new google-backstory Python client library, adding configuration files, documentation, and generated API types, as well as registering the package in the librarian configuration. The code review feedback highlights several critical issues and improvement opportunities: potential circular imports in collection.py and entity.py that should be resolved with relative imports; a bug in parse_version_to_tuple within __init__.py that incorrectly handles non-numeric version suffixes; a missing f-string prefix in a warning message; an unescaped dot in a version-parsing regular expression in setup.py; and overlapping dependency ranges in setup.py that would benefit from mutually exclusive environment markers.