fix(opcuaclient): #910 name the per-endpoint connect budget; widen it in the #816 host-name tests

Cause: the client-side PerEndpointConnectTimeout (3 s), not opc-plc. The
validate:null case is the first test the assembly runs, so it pays the
cold-process cost of the first Basic256Sha256 connect: loading the fresh
throwaway certificate, validating the server's, and the asymmetric handshake.
In the G2 full-solution run that local work used up the budget. The opc-plc
log at 13:13:50-53Z shows the discovery channel closing at 50.709, then nothing
from the client for 3 s, then OpenSecureChannel answered at 53.775 and the
client closing the channel 48 ms later. The SDK reports a wait cancelled by
that budget as BadRequestInterrupted. opc-plc auto-accepted the certificate
(--aa, "Trusting certificate ... command line option") with no reject and no
store round-trip.

- Driver: a per-endpoint budget expiry now surfaces as TimeoutException naming
  PerEndpointConnectTimeout instead of BadRequestInterrupted or a bare
  TaskCanceledException. There is no behaviour change. Unit test added
  against a silent TCP listener.
- Test: the ServerHostNameValidationTests secure options use a 15 s budget,
  the same as the browser integration tests' 10 s. Connect latency is not
  what these tests check.
- docs/drivers/OpcUaClient.md: documents what the budget covers.

docs/drivers/OpcUaClient.md

@@ -75,7 +75,10 @@ measurements; they are not fresh SDK 2.0.1 interoperability evidence.
 `EndpointUrls` (a list) takes precedence over the single-URL `EndpointUrl` and
 provides ordered **failover** — the driver tries each candidate in turn at every
 `InitializeAsync` (including the comms-loss watchdog's re-initialise), and the first to connect wins (e.g. a hot-standby pair on
-4840 / 4841). See
+4840 / 4841). Each candidate gets `PerEndpointConnectTimeout` (default 3 s) for discovery + secure channel + session. That
+budget includes **client-side** work (certificate load/validation, the asymmetric handshake), so a cold process on a busy
+host can exceed it against a healthy server; an expiry is reported as `TimeoutException: … PerEndpointConnectTimeout (3 s)`
+(#910 — the SDK alone says `BadRequestInterrupted`, which reads like a server fault). See
 `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts/OpcUaClientDriverOptions.cs`
 for every field (security policy/mode, auth type, session timeout, keep-alive,
 browse root, node/depth caps). `ReconnectPeriod` was **deleted** (#676 — unused since #670 removed the SDK reconnect