Add Kafka assignment diagnostics and prerelease package workflow

[vaital3000]

Summary

Adds targeted diagnostics around cooperative rebalance assignment handoff in Confluent.Kafka. The logs are emitted through the existing consumer log handler with the ASSIGNDIAG facility.

Also adds a GitHub Actions workflow that publishes a prerelease Confluent.Kafka package from branch kafka-assignment-diagnostics-v2.13.2 to GitHub Packages.

Diagnostic stages covered:

• rebalance callback input
• partitions assigned handler return value
• assignment list before IncrementalAssign
• Consumer.IncrementalAssign materialized list
• SafeKafkaHandle.AssignImpl managed input, native list count, and native call result

Package Publishing

Workflow: .github/workflows/publish-prerelease-package.yml

Triggers:

• push to kafka-assignment-diagnostics-v2.13.2
• manual workflow_dispatch with optional version_suffix

The workflow publishes a net8.0 prerelease package to https://nuget.pkg.github.com/dodopizza/index.json using GITHUB_TOKEN with packages: write.

Latest published package from this branch:
Confluent.Kafka version 2.13.2-dodo.kafka-assignment-diagnostics-v2-13-2.1.73238cf4

Why

We need to distinguish whether a non-empty cooperative assignment is lost in the managed callback path, the managed-to-native list construction, or after entering librdkafka.

Validation

• dotnet build src/Confluent.Kafka/Confluent.Kafka.csproj -f net8.0
• dotnet build src/Confluent.Kafka/Confluent.Kafka.csproj -f net6.0
• dotnet build src/Confluent.Kafka/Confluent.Kafka.csproj -f netstandard2.0
• dotnet test test/Confluent.Kafka.UnitTests/Confluent.Kafka.UnitTests.csproj -f net8.0
• dotnet pack src/Confluent.Kafka/Confluent.Kafka.csproj -c Release /p:TargetFrameworks=net8.0 /p:VersionSuffix=dodo.kafka-assignment-diagnostics-v2-13-2.0.localtest --output /tmp/confluent-kafka-package-test
• GitHub Actions run Publish prerelease package: passed and pushed the package

Note: full solution build was not run successfully on this macOS environment because it requires missing .NET Framework 4.6.2 targeting packs and restore assets for every example/test project.