IPC subsys refinements: connection-tracking, multi-proto-endpoint-mgmt.. etc.

[goodboy]

In follow-through from bullets collected out of #375 and #380, here
are some outstanding refined-impl-ideas for the machinery in
tractor.ipc._server which could, at the least, improve devx when
debugging (eventual) multi-tpt-proto enabled actor trees as well as
mk always maintaining a root-actor micro-registry of its subs simpler
to grok.

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Potential internals improvements / feats extension

• fill out the .ipc._server.Server.peer_tpt tables
  (implicitly) by pre-hooking into the new Endpoint (class)
  method which first registers every MsgTransport/Channel prior
  to processing and handover to the RPC layer.

  • ideally in a way that let's us granular-ly know which peers
    are on which transports and which .stream_handler_tn: Nurserys
    so we can eventually do fancy stuff like connection resetting,
    peer filtering, dynamic transport-proto swapping etc.

• multiple-transports in tandem (eventually per actor) by first ensuring
  the server layer is correct before exposing upward via
  enable_transports: list[str] to runtime-booting
  entrypoints (open_nursery()/open_root_actor()).

Test suite continuations

• more tractor.ipc unit-ish/subsys suites?
  • ipc._server.Server + low-level client connection testing,
    likely via a manual bg ipc._chan._connect_chan() connection?