Support program budget in update_program service

[sebr]

Summary

• Adds an optional budget field (integer, 0-200%) to the existing bhyve.update_program service.
• The budget scales each zone's run time: 100 leaves run times unchanged, 50 halves them, 200 doubles them.
• Service now requires at least one of start_times, frequency or budget to be provided.

Fixes #345.

Usage

service: bhyve.update_program
data:
  entity_id: switch.front_yard_usual_programming_program
  budget: 75

Test plan

• Added unit test covering budget-only updates (preserves other fields).
• ./scripts/lint and pytest tests/ pass (37 switch tests).
• Manual test: verify the B-hyve API accepts values up to 200 and that the budget change is reflected in the B-Hyve app after the program_changed event fires.