Replaces the bare-TCP AbLegacyDriverProbe with a two-phase probe:
Phase 1 is the existing TCP preflight; Phase 2 initialises a
LibplctagLegacyTagRuntime (Protocol.ab_eip + per-family PlcType) to
open a real PCCC-over-EIP session, using AbLegacyProbeOptions.ProbeAddress
("S:0") as the probe tag. Status-code discrimination mirrors the AbCip
probe: ErrorNotFound/ErrorNoMatch/ErrorBadDevice → Ok=true "controller
reachable"; transport errors → Ok=false "handshake failed".
Adds AbLegacyDriverProbeTests (5 unit tests, all green, 168 total).
Cheap-and-fast probe: open TCP socket to the configured endpoint,
close immediately. Surfaces SocketError on failure, latency on
success, "timed out" on caller cancel. Sufficient for the AdminUI
Test Connect "can we reach the host?" question. Richer protocol-
level probes (OPC UA session open, FOCAS handshake, gRPC ping)
are a documented follow-up. Each probe registered as
AddSingleton<IDriverProbe, X> in DriverFactoryBootstrap so they
flow through DI into AdminOperationsActor.
Historian.Wonderware returns a clean "TCP probe not applicable"
result because it communicates over a Windows named pipe, not TCP.
Also adds OpcUaClient + Historian.Wonderware.Client project
references to Host.csproj (both were missing from the driver
ItemGroup).
Joseph Doherty