Add preconditioning schedule calendar to Teslemetry

[Bre77]

Proposed change

Add a preconditioning schedule calendar entity to the Teslemetry integration. This is stacked on top of the charging schedule calendar PR (t-calendar-charge-schedule) and reuses the shared helper code introduced there (Schedule dataclass, get_rrule_days, async_get_sorted_schedule_events).

Key implementation details:

• Preconditioning events are instantaneous (start == end time), unlike charging schedules which have a duration
• One-time schedules do not get an rrule; only recurring schedules produce a FREQ=WEEKLY recurrence rule
• The entity is disabled by default (_attr_entity_registry_enabled_default = False)

Note: Platform.CALENDAR was registered in the base PR. PR home-assistant#145848 (tariff calendars) also adds it -- whichever merges first wins.

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 #
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