Fix deprecation warning for STATE_* constants

[arminfabritzek]

Changes:

• Replaced deprecated STATE_* constants with VacuumActivity to resolve deprecation warnings in Home Assistant Core.

Testing:

Tested on Home Assistant version 2025.1.4

Core: 2025.1.4
Supervisor: 2025.02.0
Operating System: 14.2
Frontend: 20250109.2

• Confirmed no warnings related to STATE_* constants.

Fixes #111

[kadeschs]

Still getting this:
Logger: homeassistant.components.vacuum
Source: helpers/deprecation.py:222
integration: Vacuum (documentation, issues)
First occurred: 4:44:47 PM (10 occurrences)
Last logged: 4:44:47 PM

STATE_CLEANING was used from robovac, this is a deprecated constant which will be removed in HA Core 2026.1. Use VacuumActivity.CLEANING instead, please report it to the author of the 'robovac' custom integration
STATE_DOCKED was used from robovac, this is a deprecated constant which will be removed in HA Core 2026.1. Use VacuumActivity.DOCKED instead, please report it to the author of the 'robovac' custom integration
STATE_ERROR was used from robovac, this is a deprecated constant which will be removed in HA Core 2026.1. Use VacuumActivity.ERROR instead, please report it to the author of the 'robovac' custom integration
STATE_IDLE was used from robovac, this is a deprecated constant which will be removed in HA Core 2026.1. Use VacuumActivity.IDLE instead, please report it to the author of the 'robovac' custom integration
STATE_RETURNING was used from robovac, this is a deprecated constant which will be removed in HA Core 2026.1. Use VacuumActivity.RETURNING instead, please report it to the author of the 'robovac' custom integration