[m3] Add performance notes to Keccak lookedup implementation

[HiddenAndBound]

TL;DR

Add documentation to clarify that the lookedup Keccak implementation is primarily for benchmarking purposes, not for production use.

What changed?

• Added a note at the module level indicating that the lookedup implementation serves primarily as a proxy to measure lookup performance characteristics
• Added a performance note to the Keccakf struct documentation recommending the stacked version for production use
• Added detailed comments to the Chi step implementation explaining how the AND operation works with lookups and how the merged values are used for lookup tables

How to test?

No functional changes were made, so no testing is required. The documentation can be verified by reviewing the updated comments in the code.

Why make this change?

This change helps users understand the intended purpose of the lookedup Keccak implementation and guides them toward using the more performant stacked version for production use cases. The additional comments also make the code more maintainable by explaining the purpose of the lookup-based AND operation and how the merged values are constructed for the lookup table.

[HiddenAndBound]

• [m3] Add performance notes to Keccak lookedup implementation #812 👈 (View in Graphite)
• main

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