0.5.5 — EPICS backends on epics-rs 0.24

Changed

• Bumped the EPICS backends epics-ca-rs / epics-base-rs / epics-pva-rs
  to 0.24.0 (from 0.22.x), affecting rsdm's ca/pva/calc features
  only. Three breaking API changes were adapted:
  • ConnectionEvent::Unresponsive was removed — 0.24 folds the echo-timeout
    into Disconnected (an unresponsive circuit disconnects every consumer; the
    distinction now survives only inside the client's ChannelState). rsdm
    already handled both identically.
  • The pvAccess RPC reply became RpcReply (an enum) instead of a
    (descriptor, value) tuple; its Empty variant is pvxs's no-value
    ExecOp::reply(). rsdm reads the value through RpcReply::into_value,
    treating Empty as the existing "connected, no scalar sample" case.
  • EnumInfo became #[non_exhaustive] (it gained a string_form); a test
    constructs it via EnumInfo::new instead of a struct literal.