v2.6.10

feat: wrap search DTO location fields in Optional<T>

The city, country and state properties on RandomSearchDto,
MetadataSearchDto and SmartSearchDto now use the generic Optional<T>
wrapper. This distinguishes three states that Immich treats differently:

- Unset (field omitted) -> no filter
- Null (explicit null) -> asset has no city/country/state
- Value -> match the given value

Requires generator 2.2.0 for the property override support.

Bumps version to 2.6.10.