[zeeshanlakhani]

The third part of a series of recut (and properly refactored) PRs split from #675/#696.

This exposes rdb MRIB access through mg-admin and mgadm. We introduce multicast support by way of a new API version, adding the following endpoints:

• GET /mrib/status/{imported,selected} -> lists mrib_in/mrib_loc. Every query param (group, source, vni, address family, origin) forms a logical AND combination filter, and a miss just returns an empty list.
  • No default vni (77 is OPTE/omicron policy).
  • Impossible combos (source/group IP family mismatch, an invalid source, a group/source outside the requested IP address family) are ruled out with a 400 (MribQueryError).
• PUT|DELETE|GET /static/mroute -> add, remove, and list static multicast routes.

Includes:

• mgadm adds new read-only commands: mrib status imported|selected and static get-mroutes for inspection. Omicron owns group membership and lifecycle, and programs routes through the API.
• mg-admin-client re-exports latest::mrib (as mg_admin_client::mrib) and the pinned v14 module.
• The testing feature is forwarded through mg-api-types and mg-admin-client, giving way for Omicron proptests to import the Arbitrary impls from [mcast, pt1] multicast address, source, and route key types #943 without a direct mg-api-types-versions dep.
• Handler tests, including HTTP tests for the route lifecycle through mg-admin-client and invalid query/body rejection.
• Shared test fixtures across BGP, static-route, and MRIB setups.
  • test_ctx keeps its TestDb guard for the lifetime of a context. The previous setup removed the DB directory while it was still in use in the context.
  • TestServer awaits server shutdown before DB cleanup.