chore(gpu): port fix to compression encoding

[pdroalves]

• Modifies the generation of the LUT used in decompression so that the delta is calculated with a different precision, as in the CPU implementation

closes: https://github.com/zama-ai/tfhe-rs-internal/issues/845

PR content/description

Check-list:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Relevant issues are marked as resolved/closed, related issues are linked in the description
• Check for breaking changes (including serialization changes) and add them to commit message following the conventional commit specification

[github-actions]

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[tmontaigu]

looks ok to me

[IceTDrinker]

this does not work for Torus u32 (don't know if you still support that) also this can overflow as ul (unsigned long) is not guaranteed to be 64 bits

https://en.cppreference.com/w/cpp/language/types

[pdroalves]

Indeed. Good catch.

We haven't dropped support, although we have no test or active development for u32.

I will fix this.