[Observability] Output scope

[threddy]

Introduce new output scope which just records output messages and can be linked to a parent scope. This is primarily for scenarios in which agents produce responses asynchronously.

[Copilot]

Pull request overview

Adds “output_messages” observability support across OpenTelemetry tracing and ETW logging by introducing an OutputScope, Response contract, and corresponding DTO/builder plus tests.

Changes:

• Introduces OutputScope and Response to capture/join output messages into OTEL tags.
• Adds OutputData + OutputDataBuilder and wires ETW logger support via IA365EtwLogger.LogOutput.
• Adds/extends unit tests for output scope, DTO/builder, and ETW export behavior.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/Tests/Microsoft.Agents.A365.Observability.Runtime.Tests/Tracing/Scopes/OutputScopeTest.cs	New tests validating OTEL tags + parent/child behavior for output scope.
src/Tests/Microsoft.Agents.A365.Observability.Runtime.Tests/Etw/EtwLoggingBuilderTests.cs	Adds ETW export assertions for output messages + includes LogOutput in “custom logs” test.
src/Tests/Microsoft.Agents.A365.Observability.Runtime.Tests/Etw/EtwLoggerTests.cs	Adds test ensuring LogOutput produces the expected ETW “Name”.
src/Tests/Microsoft.Agents.A365.Observability.Runtime.Tests/DTOs/OutputDataTests.cs	New test verifying OutputData.Name.
src/Tests/Microsoft.Agents.A365.Observability.Runtime.Tests/DTOs/Builders/OutputDataBuilderTests.cs	New tests verifying attribute population, timing/span IDs, and extra attribute behavior.
src/Observability/Runtime/Tracing/Scopes/OutputScope.cs	New OTEL scope implementation for output messages.
src/Observability/Runtime/Tracing/Scopes/OpenTelemetryConstants.cs	Adds OperationNames.OutputMessages.
src/Observability/Runtime/Tracing/Contracts/Response.cs	New response contract holding output messages + equality/hash.
src/Observability/Runtime/Etw/IA365EtwLogger.cs	Adds LogOutput API to ETW logger interface.
src/Observability/Runtime/Etw/A365EtwLogger.cs	Implements LogOutput and emits OutputMessages ETW event via OutputDataBuilder.
src/Observability/Runtime/DTOs/OutputData.cs	New DTO representing output operation telemetry.
src/Observability/Runtime/DTOs/Builders/OutputDataBuilder.cs	New builder creating output telemetry attributes from response + agent/tenant.