ci: derive crate version from release tag

[tbille]

Summary

• Replaces the "verify version matches tag" step with a "set version from tag" step
• The release tag is now the single source of truth for the published version — Cargo.toml is updated in-place during the workflow before cargo publish
• No more version mismatch failures between Cargo.toml and the tag

Why

The previous workflow required Cargo.toml version to exactly match the release tag, which meant a manual version bump + merge was needed before every release. This caused failures like:

Version mismatch: Cargo.toml has 0.1.0, tag is 0.0.1
Error: Process completed with exit code 1

Now the workflow simply writes the tag version into Cargo.toml before publishing, so you only need to create a GitHub Release with the desired version tag (e.g. v0.1.0) and the rest is automatic.