fix(leaderelection): survive malformed API error bodies and lock annotations

[nkbeast]

What this fixes

try_acquire_or_renew() parsed the raw API error body with json.loads and indexed straight into it:

if json.loads(old_election_record.body)['code'] != HTTPStatus.NOT_FOUND:

That assumes whatever came back is a Kubernetes Status object. Anything sitting in front of the API server — an ingress, load balancer or proxy — answers with an HTML error page, an empty payload or some other non-JSON body on a bad day, and ApiException.body can also be None. Each of those raises out of the election loop (JSONDecodeError/TypeError), and in the aio elector an empty body dies even earlier on an assert.

Leader election dying like this is the one failure mode the code exists to prevent: the controller stops renewing its lease, never calls onstopped_leading, and the workload sits in limbo instead of failing over. Reproduced locally with a lock returning a 502 HTML body — JSONDecodeError before this change, clean False retry after.

The fix

• An unparsable or missing error body is treated as "not a 404": the elector logs and retries on the next period, exactly like any other API hiccup. A clean 404 still allows lock creation, unchanged.
• The same crash existed on the read path of the ConfigMap lock: a corrupted leader-election annotation raised out of get(). It is now treated like a missing annotation so the next update rewrites a clean record.
• Both the sync and the aio implementations are fixed.

Tests

Four regression tests added: HTML error body, None body, the clean-404 create path (to prove that behaviour is untouched), and the aio elector. Full suite green locally: 436 passed, 28 skipped with the same command CI uses.

Fixed leader election crashing when the API server or an intermediary returns a malformed or non-JSON error body; the elector now treats it like any other API error and retries on the next period instead of raising. A corrupted leader-election annotation on the ConfigMap lock no longer breaks reads either.

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