fix(driver-opcuaclient): resolve High code-review findings (Driver.OpcUaClient-001..-005)

Driver.OpcUaClient-001 — ReadAsync/WriteAsync/DiscoverAsync captured the
session before acquiring _gate, so a reconnect that completed while the
operation was blocked on the gate left the wire call bound to a stale,
closed session. All three now re-read Session (and parse NodeIds) inside
the _gate critical section after WaitAsync returns.

Driver.OpcUaClient-002 — OnReconnectComplete ignored the give-up (null
session) case, permanently wedging the driver with no Faulted signal and
no reconnect loop. The give-up branch now transitions HostState to
Faulted, sets a Faulted DriverHealth with an explanatory message, and
re-arms a fresh SessionReconnectHandler (TryRearmReconnect) against the
last-known session so an always-on gateway self-heals.

Driver.OpcUaClient-003 — BrowseRecursiveAsync discarded browse
continuation points, silently truncating large remote folders.
It now loops on BrowseResult.ContinuationPoint calling BrowseNextAsync
and appending each page until the continuation point is empty.

Driver.OpcUaClient-004 — driver-specs.md §8 namespace handling was
absent. Added NamespaceMap (built from session.NamespaceUris at connect,
rebuilt on reconnect) which persists discovered NodeIds in the
server-stable nsu=<uri>;... form; reads/writes re-resolve that form
against the current session so a remote namespace-table reorder no
longer misaddresses nodes. Added the TargetNamespaceKind option +
UnsMappingTable and ValidateNamespaceKind startup enforcement.

Driver.OpcUaClient-005 — OnKeepAlive read/wrote _reconnectHandler
without a lock, racing the SDK keep-alive timer thread and leaking
handlers. The check-and-set in OnKeepAlive, the take-and-clear in
ShutdownAsync, and the dispose/re-arm in OnReconnectComplete now all
run inside the _probeLock critical section.

Adds OpcUaClientNamespaceTests (11 xUnit + Shouldly regression tests)
covering ValidateNamespaceKind and the NamespaceMap stable encoding.
Reconnect/browse wire paths remain fixture-gated per finding -015.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientFailoverTests.cs

@@ -67,6 +67,9 @@ public sealed class OpcUaClientFailoverTests
             PerEndpointConnectTimeout = TimeSpan.FromMilliseconds(500),
             Timeout = TimeSpan.FromMilliseconds(500),
             AutoAcceptCertificates = true,
+            // SystemPlatform kind needs no UNS mapping table — keeps this failover test
+            // focused on the endpoint sweep rather than §8 namespace validation.
+            TargetNamespaceKind = OpcUaTargetNamespaceKind.SystemPlatform,
         };
         using var drv = new OpcUaClientDriver(opts, "opcua-failover");