Checksum bugfix

[AstroFoil]

Fixed the length of rx buffer to fix the checksum. Also added dynamic length to ensure entire packet is calculated in checksum - Updated tests too

Pull Request (PR) Template

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• [ ] New feature (non-breaking change which adds functionality)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] Documentation Update
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• [X ] I have performed a self-review of my own code.
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• [X ] I have added tests that prove my fix is effective or that my feature works.
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