Cachix release script

[RaoulSchaffranek]

This PR replaces the legacy GitHub workflow for pushing build artefacts to the nix caches with a script that can be run locally from a developer machine.

[Copilot]

Copilot review overview

🟡 Changes recommended

Version metadata is inconsistent, and repository/tag validation can publish artifacts for the wrong commit or repository.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Verify existing release tag points to the current commit · New
• Synchronize package version metadata before release · New

What changed in this PR

Introduces a local release workflow for publishing GitHub releases and Nix artifacts.

Changes:

• Adds an interactive Cachix release script.
• Adds missing Nix Python build-system overrides.
• Advances the release version.

File	Description
package/​version	Advances the release tag version.
package/​release.sh	Builds, caches, pins, and releases the package.
nix/​kontrol-node/​build-systems-overlay.nix	Adds required Python build backends.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

The release script performs irreversible external publishing operations that cannot be safely validated without human end-to-end verification.

Review effort: Balanced
Findings: None

Resolved since last review (2)

• Verify existing release tag points to the current commit
• Synchronize package version metadata before release