Migrate to PEP 735 dependency groups

[eliotwrobson]

Summary

This PR implements support for PEP 735 dependency groups in the pyos-package-template, addressing issue #143.

Changes Made

1. Updated template/pyproject.toml.jinja

• Added conditional logic to use [dependency-groups] when use_hatch_envs=True
• Kept [project.optional-dependencies] for backward compatibility when use_hatch_envs=False
• Moved all development dependencies (dev, docs, build, tests, style, types) to the new [dependency-groups] section
• Added twine to the dependency-groups build section

2. Updated Hatch Environments

• Changed all hatch environments from features = [...] to dependency-groups = [...]
• Added builder = true to the build environment (required for Hatch 1.16+)
• Added explicit dependencies = ["twine"] to build environment as a workaround for dependency-groups not being installed in builder environments (see Builder and non-dev environments ignore dependency groups pypa/hatch#2152)
• Updated environments: build, test, docs, style, audit, and types

3. Added Tests

• Created test_hatch_deps_groups() to verify dependency-groups are properly configured when using hatch environments
• Updated test_template_suite() to use hatch run build:check instead of hatch build --clean and explicitly enable hatch environments

4. Updated Documentation

• Updated CHANGELOG.md with comprehensive notes about the migration
• Documented the requirement for Hatch 1.16+
• Explained backward compatibility when use_hatch_envs=False

Key Benefits

✅ Standards-compliant: Uses PEP 735 dependency groups instead of tool-specific optional-dependencies
✅ Less tool lock-in: Makes the template less attached to Hatch-specific configuration
✅ Forward-compatible: Leverages the newly released Hatch 1.16 support for dependency groups
✅ Backward-compatible: Maintains optional-dependencies when not using Hatch environments

Testing

• Added new test test_hatch_deps_groups() that validates the dependency-groups configuration
• Updated existing test to use the new build environment command

Notes

• Requires Hatch 1.16+ for full functionality
• When use_hatch_envs=False, the template continues to use [project.optional-dependencies] for backward compatibility

Fixes #143

cc @mathematicalmichael @Midnighter @sneakers-the-rat

[eliotwrobson]

Ran on the wrong ticket by accident 🤦🏽