Register the sample node managers through DI and finish the node manager migrations preview.4 unlocks

[romanett]

Proposed changes

Two things, on the 2.0.0-preview.4 packages master already builds against.

Every sample server registers its node managers through the container, not in its server class. Each server project gets a composition root next to its entry point (<Sample>ServerHosting.cs, services.Add<Sample>Server(...)) which registers the server as the hosted server of the stack and its node managers with the stack's server builder (server.AddNodeManager<TFactory>()). Program.Main and the tests share that one registration. The server constructors lose their AddNodeManager calls; the CreateMasterNodeManagerAsync override of the Aggregation server and the OnServerStarting override of the FileTransfer server, which registered configuration-dependent factories, are gone:

• the hosted server of the stack collects factories before it reads the configuration, so a factory type cannot take the ApplicationConfiguration in its constructor. FileTransfer gets a FileTransferNodeManagerFactory which reads the configuration on first use; Aggregation needs one factory per configured endpoint, so its composition root adds them from the container's server factory (which runs with the configuration loaded) and starts the reverse connect manager as a hosted service after the server;
• the GDS servers register the ManagedApplications and onboarding-registrar node managers as factories whose stores come from the container, and SampleGlobalDiscoveryServer creates the managers of every registered factory next to the GDS one (the GDS base server of the stack ignores registered factories);
• the UA sample server and client, which host their server through the application instance, register through AddSampleNodeManager<TFactory>() - the same registration the stack makes - which SampleApplicationHostedService now applies before it starts the server; the reference server registers the quickstart factories the same way.

AddSampleServer gains an Action<IOpcUaServerBuilder> overload. The test harness (SampleServerHost) hosts every sample in a generic host through its composition root, with the certificate stores redirected into the temporary PKI and the opc.tcp base addresses restored to localhost (the configuration loader of the stack rewrites them to the machine name). SampleServerFactories hands out the registration instead of a server factory.

The node manager migrations preview.4 unlocks (see the audit that preceded this: the pinned package now carries Objects-folder placement through CompleteConfigureAsync / UnderObjectsFolder, the root-level CreateInstance, AdditionalNamespaceUris and the cross-model generator fixes):

• Workshop Boiler, Sample Boiler, Views: the LoadPredefinedNodesAsync capture, the SetNamespaces + RegisterNamespaceManager hack and the hand-built second boiler are replaced by the attribute and builder.CreateInstance(...).Configure(n => n.UnderObjectsFolder() / OrganizedBy(...)); only the New override remains. Views moves its view membership onto the viewId overload the stack now reaches.
• MemoryBuffer becomes a [NodeManager] partial with its buffers built in Configure; the handle and monitored-item overrides stay (no fluent surface for them, Fluent node manager: no surface for on-demand (virtual) nodes; managers must still override GetManagerHandleAsync/ValidateNodeAsync UA-.NETStandard#4397 / #4399), the stale NodeSet/bsd/xsd artefacts are deleted.
• DataTypes: the instance model is source-generated from ModelDesign2.xml across the project boundary, the ModelCompiler outputs and .uanodes are deleted, the README describes the new setup.
• Aggregation: the root is linked by the fluent pass, the Status object is built through the builder, dead local-node branches are removed; the proxy's service overrides stay by design.
• StateMachines and AlarmCondition (no ModelDesign by design) become hand-written FluentNodeManagerBase subclasses driving the builder; AlarmCondition loses its on-demand handle resolution.

Documentation: Samples/Hosting/README.md and docs/TESTING.md describe the composition roots and the hosted harness.

Related Issues

• Source generator: ModelDesign structure default values are served as ExtensionObject with a null TypeId and an undecoded XML body UA-.NETStandard#4401 (recorded as a known issue in the two DataTypes tests which read a generated structure default value)
• Findings filed upstream while migrating: Source generator: [ModelDependency] payload drops AccessLevel and default values of inherited instance children UA-.NETStandard#4402, #4403, #4404, #4405; extension requests from the audit: #4397, #4398, #4399, #4400, #4388.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc.
• I have signed the CLA.
• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added necessary documentation (if appropriate).
• Any dependent changes have been merged and published in downstream modules.

Further comments

Local results on this branch: tier 0 183/183, tier 1 115/115, tier 1.5 160 passed / 3 skipped (the two recorded DataTypes expectations against UA-.NETStandard#4401 and the environment-gated UserAuthentication test), tier 2 60/61 before master was merged in; the one tier-2 failure, ClientReceivesItsNotifications(StateMachines), was a test defect fixed on master by #857, and the test passes on this branch since that merge.

Still on AsyncCustomNodeManager on purpose: DataAccess, PerfTest and HistoricalAccess wait on the SDK extensions filed above (on-demand nodes, monitored-item lifecycle hooks, historian defaults); Methods, UserAuthentication and Empty need a ModelDesign first.

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