Modernize Workshop clients (Managed Session + new Subscription Engine + streaming)

[romanett]

Sub-issue of #755.

Why

The Workshop client samples are teaching examples for specific feature areas. They all reference Samples/ClientControls.Net4 and currently use raw Session + the classic subscription/monitored-item API. They should model the v2.0 ManagedSession and new subscription engine — and, where the scenario is "wait for X / short-lived", the streaming API (IStreamingSubscription).

Scope (client folders under Workshop/)

• AlarmCondition/Client
• Boiler/Client
• DataAccess/Client
• DataTypes/Client
• Empty/Client
• HistoricalAccess/Client
• HistoricalEvents/Client
• Methods/Client
• PerfTest/Client
• SimpleEvents/Client
• UserAuthentication/Client
• Views/Client
• Aggregation/Client

Tasks

1. Managed Session: connect via ManagedSession/ManagedSessionFactory with built-in reconnect across all clients.
2. New Subscription Engine: migrate new Subscription / AddItem/ApplyChanges / per-item Notification to ISubscriptionManager/IManagedSubscription (MonitoredItems.TryAdd(name, MonitoredItemOptions, out _), ISubscriptionNotificationHandler).
3. Streaming where it fits: for event/alarm "wait-for-X" flows (AlarmCondition, SimpleEvents, HistoricalEvents) demonstrate IStreamingSubscription (SubscribeEventsAsync/SubscribeDataChangesAsync over IAsyncEnumerable).
4. Suggested order: do 1–2 representative clients first (e.g. DataAccess, AlarmCondition) to establish the pattern, then apply to the rest. Splitting into multiple PRs is fine.

References

• https://github.com/OPCFoundation/UA-.NETStandard/blob/master/docs/Sessions.md
• https://github.com/OPCFoundation/UA-.NETStandard/blob/master/docs/Subscriptions.md (Streaming subscriptions + Three-API summary)

Acceptance criteria

• Each listed client builds and runs against 2.0.x.
• No classic-engine or SessionReconnectHandler usage remains in the migrated clients.
• Alarm/event samples demonstrate the streaming API where applicable.

Dependencies

Depends on the ClientControls.Net4 modernization foundation issue.