osps-ac-03-02: use `required_types` to unblock GitLab deletion-protection semantics

[intelligent-ears]

Use the new provider_traits field to split or scope osps-ac-03-02 (branch deletion protection) so GitHub and GitLab variants can diverge cleanly instead of trying to force one rule type to handle both APIs' differing semantics.

Depends on: sub-issues 1 and 2.