[fix] Recognize full-index git patch format correctly

[uilianries]

Description of your Pull Request

Based on the PR #39, but adding a test to validate the reported bug and improved the regex to cover when a file is removed as well.

fixes #38
closes #39

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• I've tested locally that my code works.
• I've added relevant tests to verify that my code works.

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[uilianries]

The first check failed as expected, proving the reported issue #38: https://github.com/conan-io/python-patch-ng/actions/runs/18158173193/job/51682709561?pr=45#step:4:46