Finish the fluent node manager migration (#876)

[romanett]

Closes #876. The hooks the migration was waiting for landed with
OPCFoundation/UA-.NETStandard#4418 and #4442, so all five node managers that issue lists move
onto them. Master is merged in, and every NuGet package in the repository is updated - the OPC
UA preview included - in two commits of their own.

Moved off AsyncCustomNodeManager

Workshop/DataAccess, Workshop/PerfTest and Workshop/HistoricalAccess. All three serve an
address space which is computed rather than stored, over standard OPC UA types, so none of them
gets a ModelDesign - there would be no type model to declare in one. They derive from
FluentNodeManagerBase and drive the builder themselves (CreateFluentBuilder → Configure →
RegisterAuthoredNodesAsync → CompleteConfigureAsync → SealConfigurationAsync), the way
StateMachines and AlarmCondition already do, and their GetManagerHandleAsync /
ValidateNodeAsync pairs become virtual node families registered with ResolveNodes.

PerfTest needs two families: only the register variables carry a read handler, and a family
which wires one may only ever resolve variables. That read handler is new, and it is what the
move requires. The server now holds on to the node of a monitored variable, but the register
never writes into that node - it queues the changed value straight into the monitored item,
bypassing the sampling machinery - so a read of a subscribed variable would otherwise answer
with the value the variable was synthesized with.

HistoricalAccess keeps its folders and its startup items as predefined nodes; what becomes a
family is the tail which is not registered up front, a file which turns up in the archive root
and is turned into an item on the first request naming it. The family carries the two monitored
item hooks as well, which the archive items need and the live variables fall through.

Overrides whose stated reason is gone

Samples/Opc.Ua.Sample/MemoryBuffer loses GetManagerHandleAsync and its four monitored item
overrides. The tags are a virtual node family; the create hook keeps the three refusals the
sample promises (filter, index range, data encoding) and hands the stack a factory for the item
the buffer publishes into, which the stack then registers, modifies and deletes like any other
monitored item. GenerateFactory = false goes with them: the partial can read the
ApplicationConfiguration now, so the hand-written factory has no reason left to exist.

Workshop/Aggregation loses its handle resolver and validator to a virtual node family - which
also wires the browser that walks the remote address space - and its CreateMonitoredItemsAsync
and OnDeleteMonitoredItemsCompleteAsync overrides to the builder-level batch hooks.

What deliberately stays a service override

Aggregation's batched Read, Write and Call forwarding and its modify and monitoring mode hooks:
they turn one service call into one downstream service call, which the per-node fluent handlers
would undo - the opposite of what an aggregating server is for. The class remark used to say
they were waiting for #4397/#4398/#4399; it now says what they are actually there for.

HistoricalAccess's ReadAsync: it refreshes a stale archive from disk before any attribute of
an item is read, and holds the archive lock across the read so the simulation cannot change the
value fields halfway through it. A per-node read handler would only see the Value attribute.

Package updates

Two commits. The first takes everything nuget.org reports as outdated:
Microsoft.CodeAnalysis.NetAnalyzers to 10.0.401, the Microsoft.Extensions.* and
Microsoft.EntityFrameworkCore.* packages to 10.0.12, Microsoft.NET.Test.Sdk to 18.10.0 and
NUnit3TestAdapter to 6.3.0 - the last two had drifted apart between the test projects and are
now the same version everywhere. After it, every package in the repository other than the OPC UA
stack sits on its latest stable release.

The second moves the stack itself, pinned in one place in targets.props:
2.0.301.4181-preview → 2.0.312.3680-preview (SDK master 0e600c0f), eleven master builds on.
Everything it broke, it broke by having grown the thing the samples were filling in for, so each
fix is a deletion:

• SampleServerBuilderExtensions is gone. Its own summary said it held "the registrations the
  samples make on the server builder of the stack which the stack itself has no method for" - the
  stack now has all of them, so every call resolved to two candidates. AddNodeManagers grew a
  better shape on the way: the loaded ApplicationConfiguration is handed to the callback instead
  of being resolved from the container, which is what ConfiguredNodeManagerFactories and the loop
  over it in SampleServerFactory existed for. Both are gone too.
• NodeBrowser grew the async browse seam the Aggregation Browser was waiting for, in so many
  words ("There is no async browser seam in the stack to migrate to yet"). NextAsync is an
  override now, so the asynchronous browse and translate paths await the call to the aggregated
  server instead of blocking a request worker on it.
• The model generator emits a protected constructor taking the namespace URIs, which is what
  TestData had a hand-written constructor and GenerateFactory = false for. The sample names its
  second namespace in AdditionalNamespaceUris now, takes the generated factory, and creates the
  test system in an override of the three-argument LoadPredefinedNodesAsync.

Verified against the packages of the nuget-publish run which produced that version (run
34435263403, its opcua-packages-34435263403 artifact used as a local folder feed, because
GitHub Packages cannot be queried without a token). A reviewer with feed access should confirm
2.0.312.3680-preview is the version they want - it is simply the newest master build at the
time of writing.

Verification

Whole solution rebuilds with the same set of warning codes as before either bump, 0 errors.
All five test tiers, on the new SDK:

• SampleNodeManagers.Tests - 192 passed, 1 pre-existing skip
• SampleServers.Tests - 126 passed
• SampleClientModels.Tests - 445 passed, 3 skipped
• SampleClients.Tests - 65 passed
• SampleConfiguration.Tests - 247 passed

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