Restore config entry version 4 migration

[kagithd]

Problem

Release 0.9.20 includes the configurable TLS verification option, but
LoxoneFlowHandler.VERSION is still 3 and the migration only handles versions
1 through 3. Existing entries that were already migrated to version 4 therefore
fail to load:

Config entry ... has version 4 which is higher than the current version 3

Fix

• Restore config entry version 4.
• Migrate version 3 entries by adding the verify_ssl default.
• Use Home Assistant's supported async_update_entry API for all migration
  steps.
• Extend the focused migration tests.

No unrelated integration behavior or manifest version is changed.

Validation

• python -m compileall -q custom_components/loxone
• Focused structural migration validation
• Installed commit 1de8ec9 from HACS on Home Assistant 2026.7.4
• Tested against Loxone Miniserver 17.1.6.30
• Config entry changed from migration_error to loaded
• 57 entities and 36 devices registered
• No new PyLoxone or migration errors after restart

The full local pytest run was unavailable because the pinned Home Assistant
2026.6.4 test dependency requires Python 3.14.2 while the available local
interpreter is Python 3.13. CI can run the added focused tests in the project
environment.

[JoDehli]

@kagithd this is still marked as draft? When you you finish it?