v2.2.2

Follow-up to #27. When I folded the copy-pasted retry loop into _get_json_with_retry, I flagged that its retry path had no test coverage — the fake aiohttp session never raised, so only the happy path was exercised. Same was true of list_gcr_tags, which kept its own retry loop (it has a pre-raise_for_status 401 check).

Test-only, no source changes.

Adds:

• _get_json_with_retry — recovers after transient errors; exhausts max_retries then re-raises; sleeps with exponential backoff (2**0, 2**1, …) between attempts and not after the last; max_retries is honoured.
• list_gcr_tags — a 401 returns [] immediately with no retry/sleep; transient errors are retried then succeed; after exhausting retries the outer handler swallows the raise and returns [].
• list_ghcr_tags — a transient error on the tags request recovers through the shared helper.

Infra: a SequencedSession fake (each URL maps to a queue of outcomes, so a call can fail then succeed) and an autouse fixture that stubs asyncio.sleep and records the delays instead of waiting.

pytest 153 passed · ruff check + ruff format --check clean.