legal: Please add SDPX header to comply reuse

I have noticed that some files of projects are vendored in other places, to improve SBOM it would be nice to consider to add SPDX headers in all projects file, Any hints on copyright holders ?

Please confirm thoses lines are correct:

```
* SPDX-FileCopyrightText: kokke
* SPDX-License-Identifier: Unlicense
```

Review the repository's project files and existing license information before deciding which files need SPDX headers. Confirm the copyright holder and identifier with the maintainer; done means the applicable files contain agreed, correct SPDX metadata.

Written by the indexing model from the issue text.