fix: remove shared solve-group from environments

[prem-2006]

Fixes #64

Summary

Fixes a cross-platform dependency resolution issue in pixi.toml that caused pixi install and pixi run to fail on Windows and Linux.

The problem occurred because the default environment and the macos-mlx environment shared the same solve-group, which caused Pixi to attempt resolving macOS-specific dependencies on non-macOS systems.

Removing the shared solve-group allows Pixi to resolve each environment independently.

Context

The default environment is intended to be cross-platform, while the macos-mlx environment contains Apple Silicon–specific dependencies such as mlx-audio.

Both environments were configured with:

solve-group = "default"

When environments share a solve-group, Pixi generates a single dependency resolution for them. This caused Pixi to attempt resolving macOS-only dependencies on Windows and Linux, resulting in the following error:

failed to solve the pypi requirements of environment 'default' for platform 'osx-arm64'

Changes

• Removed solve-group = "default" from the default environment
• Removed solve-group = "default" from the macos-mlx environment
• Allowed Pixi to resolve environments independently

No dependency versions or packages were changed.

How you Tested

1. Ran pixi install on a non-macOS system
2. Verified dependency resolution completes successfully
3. Ran pixi run to confirm the project builds and runs correctly

Breaking Changes

• No breaking changes
• Breaking change (describe below)

Testing

• Verified pixi install and pixi run work correctly

PR Hygiene

• PR is small and focused
• No unrelated commits

🧩 Additional Notes for Reviewers

This change only affects dependency resolution behavior in Pixi and improves cross-platform compatibility without modifying any dependencies.