refactor: Simplify cron scaler code

[joelsmith]

The current cron scaler code creates a cron object and starts it (which creates a goroutine and a lot of data to manage a cron engine) just so that it can find the next activation time. It also re-parses the cron strings on each iteration. This update only parses on creation of the trigger, then uses the cron schedule object directly to get the next activation time.

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