fix(Google Calendar node): Correctly set dtstart for recurrence rules in addNextOccurrence function

[marcelreschke]

Summary

Fixes #12262 issue in the Google Calendar node, where the nextOccurrence field was not preserving the original event's time when calculating recurring events. The changes include:

• Fixed time calculation in addNextOccurrence function by initializing RRule with proper dtstart option
• Added comprehensive test suite to verify time preservation and edge cases

It ensures the next occurrence maintains the same time as the original event

Related Linear tickets, GitHub issues, and Community forum posts

Fixes #12262

Review / Merge checklist

• PR title and summary are descriptive
• Tests included
• No documentation update needed
• Non-critical bug fix; PR doesn't need to be labelled release/backport

[CLAassistant]

All committers have signed the CLA.

[Joffcom]

Hey @marcelreschke,

Thanks for the PR, We have created "GHC-605" as the internal reference to get this reviewed.

One of us will be in touch if there are any changes needed, in most cases this is normally within a couple of weeks but it depends on the current workload of the team.