Add comprehensive documentation for ComplexTypes library

[Copilot]

Proposed changes

Adds documentation for Opc.Ua.Client.ComplexTypes library to address the complete lack of documentation and examples for working with custom structures and enumerations in OPC UA.

Created Docs/ComplexTypes.md (660 lines) covering:

• Core concepts: Type discovery, loading mechanisms (DataTypeDefinition, binary/XML dictionaries), dynamic .NET type generation
• Basic operations: Loading types, reading/writing complex values, property access patterns
• Advanced usage: Namespace-specific loading, type introspection, custom factories, telemetry integration
• Patterns: One-time loading, lazy loading, batch operations
• API reference: Complete signatures for ComplexTypeSystem, IComplexTypeProperties, ComplexTypePropertyInfo
• Troubleshooting: Common issues (types not loading, ExtensionObject encoding, performance)

Example workflow:

// Load custom types
var complexTypeSystem = new ComplexTypeSystem(session);
await complexTypeSystem.LoadAsync();

// Read structured data
DataValue dataValue = await session.ReadValueAsync(nodeId);
var complexType = (IComplexTypeProperties)((ExtensionObject)dataValue.Value).Body;

// Access properties by name or index
complexType["Temperature"] = 25.5;
complexType["Pressure"] = 101.3;

// Write back
await session.WriteAsync(null, writeValues, CancellationToken.None);

Updated Docs/README.md: Added ComplexTypes reference, fixed inconsistent ECC Certificates path.

Related Issues

• Fixes ComplexType - Lack of Documentation #1874

Types of changes

• 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

Documentation follows existing structure (similar to PubSub.md, Observability.md). All API signatures verified against implementation. No code changes required.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>ComplexType - Lack of Documentation</issue_title>
<issue_description>### Type of issue

• Bug
• Enhancement
• Compliance
• Question
• Help wanted

Current Behavior

Documentation, Examples, etc... are inexistent regarding ComplexType

Expected Behavior

Documentation, simple examples exists for the ComplexType usage.

I want to be able do Write and Read Structs from a Client to a Server in a one shot way.
I'm unable to figure out the way to do this.

Steps To Reproduce

No response

Environment

No response

Anything else?

No response</issue_description>

<agent_instructions>Please add a documentation file describing how to use the Opc.Ua.Client.ComplexTypes packages and what functionality it provided</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@mregen Hi @deinok, complex type bug fixes and updates are planned for the next release.

• Fixes ComplexType - Lack of Documentation #1874

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