Retarget adapter-resolution e2e tests off the temporary private repo to a public fixture #1655

Follow-up to #1654, which introduces the temporary private-repo e2e test setup described below — it is not yet on main; retarget to a public repo once #1654 merges.

Problem

The adapter-resolution e2e tests in test/backends/test_adapters/test_adapter_resolution_e2e.py point at a temporary private repo, ajbozarth/granitelib-rag-r1.0 (a weights-stripped copy of ibm-granite/granitelib-rag-r1.0 with prompt io.yaml files added), pinned to a specific SHA. Because the repo is private, the tests xfail rather than run for anyone without read access — including CI's public-only token and any other developer's token — via the require_hf_token() marker plus the _xfail_if_test_repo_unreadable autouse fixture. They run normally only for a developer with access to that personal repo.

This is a deliberate, documented stopgap (there is a TODO at the top of the file), but a bare in-code TODO can linger silently: the tests give no real signal in CI, and the SHA pin, private-repo dependency, and xfail guard stay in place until someone removes them. This issue tracks that removal.

What needs to happen

• Publish or identify a public repo that carries the same layout the tests exercise: the prompt io.yaml files under the adapter-function subpaths, for the model slots the tests reference (granite-4.2-3b, granite-4.2-8b, and the any slot).
• In test/backends/test_adapters/test_adapter_resolution_e2e.py, repoint _TEST_REPO and update _TEST_SHA to the public repo.
• Remove the temporary access guard once the repo is public: the _xfail_if_test_repo_unreadable autouse fixture and its _test_repo_readable() helper, plus the require_hf_token() marker if the public repo needs no token. The guard is grouped under the file's TODO comment for easy removal.
• Repoint any e2e tests the OpenAI/Ollama prompt-fallback follow-up adds against the same fixture repo.

Acceptance criteria

• The adapter-resolution e2e tests run (not xfail) under CI's token.
• No remaining reference to ajbozarth/granitelib-rag-r1.0 or a personal-repo SHA pin in the test suite.
• The _xfail_if_test_repo_unreadable guard and its TODO are removed.