ci: add test coverage enforcement to all library packages

[rororowyourboat]

Summary

• Adds pytest-cov>=6.0 to dev dependencies for gds-viz, gds-games, gds-stockflow, and gds-control
• Configures 80% coverage threshold (matching gds-framework) for all four packages
• Coverage reports automatically via pytest addopts — no CI workflow changes needed
• Skips gds-examples (tutorial package, not a library)

Package coverage config

Package	Source	Threshold
gds-framework	gds	80% (existing)
gds-viz	gds_viz	80% (new)
gds-games	ogs	80% (new)
gds-stockflow	stockflow	80% (new)
gds-control	gds_control	80% (new)

Test plan

• CI tests pass for all packages
• Coverage reports appear in test output
• All packages meet the 80% threshold

[Copilot]

Pull request overview

This PR establishes consistent test coverage enforcement across all library packages in the gds-core monorepo by adding pytest-cov configuration with an 80% coverage threshold to match the existing standard in gds-framework.

Changes:

• Added pytest-cov>=6.0 as a dev dependency to four library packages
• Configured 80% coverage threshold with consistent settings across all packages
• Coverage enforcement is integrated into pytest via addopts (no CI workflow changes required)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/gds-viz/pyproject.toml	Adds pytest-cov dependency and configures 80% coverage for gds_viz package
packages/gds-stockflow/pyproject.toml	Adds pytest-cov dependency and configures 80% coverage for stockflow package
packages/gds-games/pyproject.toml	Adds pytest-cov dependency and configures 80% coverage for ogs package
packages/gds-control/pyproject.toml	Adds pytest-cov dependency and configures 80% coverage for gds_control package

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[rororowyourboat]

Superseded by #42 (combined merge branch)