Incus: Cross-project instance copy bypasses target project restrictions via TOCTOU in config merge

Incus is a system container and virtual machine manager. Prior to version 7.3.0, when copying an instance across projects, the project restriction check (`AllowInstanceCreation`) runs BEFORE the source instance's configuration is merged into the request. Dangerous configuration keys (including `security.privileged`, `raw.lxc`, `raw.apparmor`) from the source instance are merged AFTER the check passes, bypassing all project restrictions on the target project. Version 7.3.0 patches the issue.