Update CBOR generators to support event streaming

[muhammad-othman]

Description

• Updated EventStreamPublisherMarshaller.tt to support publishing CBOR payloads.
• Updated EventStreamOutputGenerator.tt to support reading CBOR response.

Motivation and Context

DOTNET-8164

Testing

• Since there are no services that supports event streaming with CBOR I've generated CloudWatchLogs and TranscribeStreaming services with CBOR protocol and validated the generated code.
  • The generated services can be found in this testing branch.
  • EventStreamPublisher generated example

    aws-sdk-net/sdk/src/Services/TranscribeStreaming/Generated/Model/Internal/MarshallTransformations/MedicalScribeInputStreamPublisherMarshaller.cs

    Line 60 in f664606

    var writer = CborWriterPool.Rent();

  • EventStreamOutput generated example https://github.com/aws/aws-sdk-net/blob/muhamoth/DOTNET-8164-cbor-event-streaming-support-testing/sdk/src/Services/CloudWatchLogs/Generated/Model/StartLiveTailResponseStream.cs#L55
• DRY_RUN-04e5355c-d6c0-4e41-baa3-ea261d74fb91.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[Copilot]

Pull Request Overview

This PR adds support for CBOR (Concise Binary Object Representation) protocol to event streaming functionality in the AWS SDK for .NET, enabling the generation of event stream publishers and consumers that can handle CBOR-encoded payloads.

• Introduces CBOR-specific marshalling and unmarshalling for event stream events
• Updates code generators to produce CBOR-compatible event stream publishers and output generators
• Adds new utility methods for converting event stream messages to appropriate contexts

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
EventStreamUtils.cs	Adds utility method to convert event stream messages to generic streams
IEventStreamPublisher.cs	Changes EventStreamRequest access modifier from private to protected
Member.cs	Updates type unmarshaller instantiation logic for CBOR protocol support
StructureGenerator.tt	Adds CBOR namespace imports and fixes event interface inheritance
EventStreamOutputGenerator.tt	Implements CBOR support for event stream output generation
EventStreamPublisherMarshaller.tt	Adds CBOR marshalling support for event stream publishers
JsonRPCStructureUnmarshaller.tt	Fixes null reference check for event payload members
CborStructureUnmarshaller.tt	Fixes event payload member handling and structure cleanup
CborSimpleTypeUnmarshaller.cs	Adds new DateTime unmarshaller for epoch milliseconds
CborEventStreamPublisher.cs	New base class for CBOR event stream publishers

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[Copilot]

This null-conditional operator may introduce inconsistent behavior. If RequestStructure is null, the string.Equals will never match, potentially changing the logic from the original code which would have thrown a NullReferenceException.

Suggested change

	if (this.ModelShape.IsEventStream && this.model.Operations.FirstOrDefault(x => string.Equals(this.OwningShape.Name, x.RequestStructure?.Name)) != null)
	if (this.ModelShape.IsEventStream && this.model.Operations.FirstOrDefault(x => string.Equals(this.OwningShape.Name, x.RequestStructure.Name)) != null)

[muhammad-othman]

I did that because I faced a an operation without a request structure in a testing service.

[Copilot]

The reader.ReadEndMap() call has been moved outside the conditional block, but it should only be called when a map was actually started. This could cause issues when handling event structures with explicit payload members.

[muhammad-othman]

No it wasn't, the duplicate if conditions was merged in one condition.

[peterrsongg]

looked at the generated branch. looks good.

[ashishdhingra]

Looks good at high level. Nice work on modifying T4 files.