fix(cron): prevent duplicate executions and enhance type safety

[juddisjudd]

This PR addresses two key issues with the cron implementation:

1. Fixed unintentional duplicate executions by:

   • Adding lastRun timestamp tracking for each task
   • Adding a 60-second cooldown check between executions
   • Adding debug logging for prevented duplicates

2. Enhanced type safety and validation:

   • Added proper type annotations for special cron expressions (like 'L' for last day)
   • Added support for named day/month formats (mon-fri, jan,dec)
   • Improved validation for ranges and step values
   • Enhanced error messages for invalid expressions