verify sha256 checksums for windows users.

[KASR]

feat: Add PowerShell script to verify file hashes for Windows users

This commit adds a PowerShell script that can be used to verify the hash sums of model files on Windows. The script reads the SHA256SUMS file with the expected hash sums and filenames, calculates the SHA256 hash of each file using certUtil, and compares it with the expected hash.

The output is a table with the filename, valid checksum (if the hash matches), and file missing (if the file is not found).

edit: I've provided a small how-to in the readme file.

[sw]

Good idea. I can't test this as I'm not using Windows. Please consider moving this to scripts/ and updating the readme, so Windows users will know what to do.

[KASR]

@sw I've made the suggested changes.

It would be great if some other windows user could test the script on his machine.

[KASR]

I will close this PR and open a new one where the verification script uses python, so that we the proposed solution is independent of the operating system.