Return type deprecation notices need to be addressed before php9

[nolmac]

When using the library with php8+, you will may see deprecation notices like:

Return type of RusticiSoftware\Cloud\V2\Model\LaunchLinkRequestSchema::offsetExists($offset) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

We should update internal return types to avoid this as they will be eventually enforced in php9.0. More context: https://stackoverflow.com/questions/71133749/reference-return-type-of-should-either-be-compatible-with-or-the-re