Switch from poetry to PDM, update repo name

[magnuslo]

This pull request introduces significant updates to modernize the project, including renaming the package, updating the build and publishing workflow, and revising documentation and configuration files. The most important changes are grouped below:

Project Renaming and Documentation Updates:

• The project has been renamed from PyAPNs2/apns2 to mopyapns, with all relevant references in README.md and pyproject.toml updated accordingly. This includes package name, installation instructions, repository URLs, and usage examples. [1] [2] [3] [4] [5]
• The minimum supported Python version is now 3.10 (was 3.9), and the documentation and classifiers have been updated to reflect this change. [1] [2]

Build and Publishing Workflow Modernization:

• Switched the build system from Poetry to PDM, updating pyproject.toml and test/development dependencies accordingly. [1] [2]
• Added a new GitHub Actions workflow (.github/workflows/pypi_publish.yml) to automate building and publishing the package to PyPI on release or manual trigger.

Feature and Usage Enhancements:

• Updated the usage example in README.md to demonstrate sending notifications with a specific interruption level (iOS 15+).

These changes collectively modernize the project infrastructure, clarify its identity, and improve the developer experience.