Add release workflow for building and publishing Pixi

[akhanf]

This pull request updates the project's build system and continuous integration configuration to use Hatchling and Pixi for building and publishing the package. The main goals are to modernize the build process and streamline publishing without the need for stored secrets.

Build system migration:

• Switched the build backend from setuptools to hatchling in pyproject.toml, updating the build-system section accordingly.
• Removed old setuptools configuration and added [tool.pixi.package] and related Pixi build configuration to support the new build process.

Continuous integration and publishing:

• Added a new GitHub Actions workflow in .github/workflows/release-workflow.yml that uses Pixi to build and publish the package to the specified channel, leveraging OIDC for authentication and removing the need for stored secrets.

These changes help standardize and secure the build and release process for the project.