ci: serialize package publish workflows - #300

Summary

Closes #298.

The package publishing workflows could start concurrently when consecutive commits touched the same package path. This can race on package versions or produce redundant registry publishes.

Changes

• Add a workflow-specific concurrency group to all nine package publishing workflows.
• Set cancel-in-progress: false so releases queue and remain ordered.
• Include the Helm chart workflow, which was also missing the guard.

Compatibility

This only affects scheduling of publish workflows. Existing triggers, jobs, permissions, and release behavior are unchanged; overlapping runs now queue per workflow instead of running concurrently.

Validation

• Parsed all nine changed workflow files with PyYAML 6.0.2.
• Verified each file defines a unique concurrency.group and cancel-in-progress: false.
• git diff --cached --check reported only pre-existing line-ending/EOF formatting warnings from the sparse checkout.

Notes

A full repository test suite was not run because this change only modifies GitHub Actions workflow scheduling.