BED-9519: add adaptive GraphQL page sizing

[jaredcatkinson]

Summary

• add a generic adaptive GraphQL pagination helper that retries terminal 502/504 pages at 100, 50, then 25 items
• update repositories_graphql to use adaptive page sizing and log the cursor plus final failed page size
• add coverage for page-size fallback, recovery probes, degraded mode, and terminal smallest-page failures

Testing

• uv run pytest tests/test_repository_rulesets.py tests/test_helpers.py
• uv run ruff check src/openhound_github/helpers.py src/openhound_github/resources/organization.py tests/test_repository_rulesets.py
• uv run pytest --ignore=tests/test_github_rest_client.py --ignore=tests/test_github_retry.py

Notes

• Full uv run pytest still hits pre-existing collection errors in tests/test_github_rest_client.py and tests/test_github_retry.py because they import modules not present on main.
• The broader suite also has an existing order-sensitive tests/test_org_scim_resources.py::test_org_scim_users_are_bound_to_successful_scim_scope failure when run in the full suite; it passes in isolation and alongside the touched repository tests.

[JimSycurity]

PR 47 may have conflicts with this. Otherwise fine.