feat(irmin,pds,atp,rpmsg): on_listen callback, PDS cleanup, interop test
- xrpc_server: add on_listen callback with actual bound port (supports port 0)
- pds: register Eio.Switch.on_release for DB close in create/open_
- irmin: use on_listen in cmd_serve, close PDS in cmd_init, add interop cram test
- rpmsg: rename test_endpoint → test_rpmsg for consistency