chore: bump icicle to v2.6.0

[mrain]

no issue related.

This PR:

• bump icicle deps to v2.6.0
  • HostOrDeviceSlice is now a trait. Occurrences are changed to concrete types now.
  • For Bn254 curve impl
    • commit_on_gpu now assume that the input scalars are in normal form instead of montgomery form.
    • now load_poly_to_gpu has one memory copy instead of free as before
    • these are because, icicle field impl now uses u32 limbs instead of u64 limbs as in arkworks.
• add GPU stress test for memory leakage/fragmentation

This PR does not:

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• Targeted PR against correct branch (main)
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added relevant changelog entries to the CHANGELOG.md of touched crates.
• Re-reviewed Files changed in the GitHub PR explorer

[alxiong]

thanks @mrain for taking the initiative to upgrade our icicle dep! 👍