fix(detectors): Guard against null queryObj in cron monitor list

[sentry]

This PR fixes a TypeError: Cannot read properties of null (reading 'environments') that occurred in the cron monitor list (/monitors/crons/).

The root cause was that the API could return a CronDetector object where dataSources[0].queryObj was null, even though the TypeScript type CronMonitorDataSource declared queryObj as non-nullable. This led to a runtime crash when accessing properties like environments on a null queryObj.

The fix involves:

1. Updating the CronMonitorDataSource type in static/app/types/workflowEngine/detectors.tsx to correctly reflect that queryObj can be null.
2. Adding optional chaining (?.) and null guards in static/app/views/detectors/list/cron.tsx for all accesses to queryObj and its properties, specifically in the VisualizationCell and the environment-label column's renderCell function. This ensures the UI gracefully handles cases where queryObj is null without crashing.

Legal Boilerplate

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Fixes JAVASCRIPT-39QF

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}

[github-actions]

📊 Type Coverage Diff

Metric	Before	After	Delta
Coverage	93.93%	93.93%	±0%
Typed	134,713	134,714	🟢 +1
Untyped	8,704	8,705	🔴 +1

🔍 1 new type safety issue introduced

Non-null assertions (!) (1 new)

File	Line	Detail
static/app/views/detectors/list/cron.tsx	88	cronId!

This is informational only and does not block the PR.

[malwilley]

This is more of a data integrity issue, so it's better that we delete the offending models and prevent the data from being corrupted instead. Making this an optional field isn't really correct and it will cause the code to be much more gnarly