feat: Implement schedule block data contract for Scheduled Climate

[stupiddevmonkey]

• Add ScheduleBlock class to manage climate settings for scheduled blocks.
• Introduce ClimateCommand and BlockPlan classes for command handling.
• Implement helper functions for planning HVAC modes, temperatures, fan modes, and humidity settings.
• Create diagnostics support for Scheduled Climate to provide config entry diagnostics.

test: Add unit tests for schedule block functionality

• Implement tests for ScheduleBlock and build_plan functions.
• Validate behavior for HVAC mode, temperature ranges, and command generation.
• Ensure proper handling of unsupported features and out-of-range values.

feat: Add frontend support for schedule management

• Create schedule helpers for managing time ranges and blocks.
• Implement validation for draft blocks and ensure proper serialization for storage.
• Add utility functions for converting legacy time formats to the new structure.

test: Add migration tests for Scheduled Climate config entries

• Ensure legacy time formats are preserved during migration from version 1 to 2.
• Validate that entries without legacy times migrate correctly without issues.