Fix slow event state updates for remote calendar

[allenporter]

Proposed change

Fix slow event state updates for remote calendar that currently log the following error.

Updating state for calendar.xxxxx (<class 'homeassistant.components.remote_calendar.calendar.RemoteCalendarEntity'>) took 1.126 seconds. Please create a bug report at https://github.com/home-assistant/core/issues?q=is%3Aopen+is%3Aissue+label%3A%22integration%3A+remote_calendar%22

This is similar to other fixes to local calendar in the past.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Remote Calendar slow updates #159051
• This PR is related to issue:
• Link to documentation pull request:
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
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• Tests have been added to verify that the new code works.
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[home-assistant]

Hey there @Thomas55555, mind taking a look at this pull request as it has been labeled with an integration (remote_calendar) you are listed as a code owner for? Thanks!

Code owner commands

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[Copilot]

Pull request overview

This PR fixes a performance issue in the remote_calendar integration where updating the calendar entity state was taking over 1 second, causing Home Assistant to log slow update warnings. The fix aligns the remote_calendar implementation with the pattern already used in local_calendar.

Key changes:

• Eliminated redundant Timeline object creation and storage by caching the next event directly
• Changed the event property from computing the next event on-demand to returning a pre-computed cached value
• Modified async_update to compute and store the next CalendarEvent directly instead of storing an intermediate Timeline object