Migrate Workshop/HistoricalAccess server Node Manager to AsyncCustomNodeManager

[romanett]

Part of #753.

Goal

Migrate the HistoricalAccess Workshop server sample to AsyncCustomNodeManager, including its historian read/update paths. It builds its address space by hand (no generated model), so Step 2 (Fluent) does not apply.

Scope

• Workshop/HistoricalAccess/Server/HistoricalAccessNodeManager.cs — HistoricalAccessServerNodeManager : CustomNodeManager2
• Workshop/HistoricalAccess/Server/HistoricalAccess Server.csproj and its node-manager registration
• Related history helper types under Workshop/HistoricalAccess/Server

Do not touch the client or the Tester project.

Step 1 — AsyncCustomNodeManager

1. Base class CustomNodeManager2 → AsyncCustomNodeManager; constructor base(server, configuration, <namespaceUri>).
2. CreateAddressSpace → override async ValueTask CreateAddressSpaceAsync(...); LoadPredefinedNodes → LoadPredefinedNodesAsync.
3. Convert history handling to the async history interfaces: IHistoryReadAsyncNodeManager / IHistoryUpdateAsyncNodeManager (raw data, modified, processed/aggregate reads, and history update/delete). Convert read/write callbacks to async handlers.
4. Remove lock (Lock) blocks — use base async locking.
5. Register via IAsyncNodeManagerFactory.

Acceptance criteria

• HistoricalAccessServerNodeManager derives from AsyncCustomNodeManager; history read/update goes through the async interfaces; no CustomNodeManager2 / lock (Lock) remains.
• HistoricalAccess Server builds/starts; the client performs raw/processed history reads and history updates successfully.

References

• docs/AsyncServerSupport.md (UA-.NETStandard) — async history-read/update interfaces.