ci(license): add license header check for .rs files

[riccardo-negri]

No description provided.

[riccardo-negri]

License check works as expected. See https://github.com/network-analytics/NetCalyx/actions/runs/30550515470/job/90897767302?pr=20.

[Copilot]

Pull request overview

Adds a CI guardrail to enforce Apache 2.0 license headers on Rust files touched in pull requests, with additional rules around preserving legacy NetGauze attribution when present.

Changes:

• Introduces a new license job in CI to run only on pull_request events and validate headers on changed *.rs files.
• Adds .github/scripts/check_license.py to validate the required header format and ensure NetGauze attribution lines aren’t removed when they existed in the base ref.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/ci.yml	Adds a PR-only job that identifies changed Rust files and runs the license checker.
.github/scripts/check_license.py	Implements header validation and base-ref comparison logic for NetGauze attribution preservation.

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[riccardo-negri]

Retested after review. Works as expected: https://github.com/network-analytics/NetCalyx/actions/runs/30554296689/job/90910745785?pr=20

[ustorbeck]

• When a file is renamed or copied and substantially rewritten git will detect it as a new file and the license check will fail with "new file must not have a NetGauze Authors copyright line" which it should not. Either reduce the similarity threshold for git or maybe drop the check for the NetGauze header in new files.
• The script uses git porcelain commands (git show, git diff) where the output format is not guaranteed to be stable. Better use git plumbing commands like git cat-file instead.