Handle ossutil JSON timing output

[Open-Squilla]

Scope

• Parse the JSON document emitted by ossutil API commands while accepting its trailing elapsed-time line.
• Reject unexpected trailing output so the OSS mirror remains fail-closed.
• Use the parser for bucket versioning and object version-ID readback.

Evidence

• Reproduced with pinned ossutil 2.3.0 against the configured Beijing bucket: the command returned a valid JSON object followed by 0.xxxxxx(s) elapsed.
• The failed mirror run 32446835820 had already passed credentials, release, and source audits; it failed before upload at the JSON parser.

Tests

• uv run python -m pytest tests -q — 53 passed
• python3 -m ruff check scripts tests — passed
• Direct macOS-arm64 ossutil probe validated both versioning and head-object responses through the new parser.

Safety

• No release assets or OSS objects were modified by the failed run.
• No secrets are included in this PR.