fix: parse cron observability events (#440)

[agent-think]

Requested by @mattzcarey

Closes #440

What was wrong

apps/workers-observability/src/types/workers-logs.types.ts required $workers.outcome for every telemetry event. The Workers Observability API legitimately omits that field (as well as the already-optional timing fields) for eventType: "cron", so the V4 response parser rejected the entire events response before query_worker_observability could return it.

There was no existing PR for #440, and main still contained the required field when this change was prepared.

What changed

• make $workers.outcome optional, matching the upstream event shape while preserving validation when it is present
• document cron rather than scheduled as an example $metadata.origin value
• add a regression fixture that parses the full V4 response shape for a cron event with no outcome or timing fields
• add a patch changeset for workers-observability

Testing

• Confirmed the new regression test fails before the schema change with the reported expected string, received undefined error at $workers.outcome.
• pnpm exec prettier --check apps/workers-observability/src/types/workers-logs.types.ts apps/workers-observability/src/workers-logs.types.spec.ts .changeset/fuzzy-jobs-observe.md — passed
• pnpm --filter workers-observability check:lint — passed
• pnpm --filter workers-observability check:types — passed
• pnpm --filter workers-observability test — passed (2 files, 9 tests)
• pnpm exec changeset status — passed

Demo

Demo URL (expires after 60 mins): https://issue-440-cron-observability-demo.palm-pepperberry.workers.dev

Open the page and press Parse cron event; it displays PASS and the parsed cron event even though outcome, cpuTimeMs, and wallTimeMs are absent. The demo runs the packed workers-observability schema from this branch (plus its packed workspace dependency).

🤖 generated by the pr-agent — please review carefully

[mattzcarey]

@agent-think did you check the open api spec