Increase SMALL_VALUE_BITS to 29 and rename builtin-specific bound.

[ilyalesokhin-starkware]

SMALL_VALUE_BITS increases from 27 to 29 for general small values. The builtin n_uses range check keeps the tighter 27-bit bound under the new name BUILTIN_USAGE_BITS, since builtin_start + n_uses * instance_size must not overflow M31_P.

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Note

Medium Risk
Touches constraint bit-decomposition and range-check bounds used in proof verification; incorrect bounds could allow invalid public data or break compatibility with existing traces.

Overview
Updates Cairo AIR statement constraints to treat general “small” public values as 29-bit instead of 27-bit, including updating the value-to-limb splitter to output 4×9-bit limbs and using it for public memory and safe-call initialization logup terms.

Keeps builtin n_uses range checks at a tighter 27-bit bound under the new BUILTIN_USAGE_BITS constant, and adjusts the associated overflow assertion and extraction calls to match the new split between 29-bit addresses/values and 27-bit builtin usage counts.

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PR Summary

Medium Risk
Touches AIR constraint bit-bounds and limb encoding used in public memory logup and builtin usage checks; incorrect bounds could cause verification failures or unintended acceptance/rejection of proofs.

Overview
Updates Cairo AIR statement constraints to treat “small” public values as 29-bit instead of 27-bit.

This renames and refactors the limb-splitting helper to split_29bit_value_to_9bit_limbs (now producing 4×9-bit limbs) and threads it through segment-range and safe-call public memory logup terms.

Builtin usage range checks are decoupled from the new 29-bit bound via a new BUILTIN_USAGE_BITS = 27, updating the extract_bits calls and overflow assertion/documentation to ensure start + n_uses * instance_size stays below M31_P.

^{Reviewed by Cursor Bugbot for commit bf0b3a8. Bugbot is set up for automated code reviews on this repo. Configure here.}