refactor: replace hardcoded byte indices with WORD_SIZE in ram_init_final

[letmehateu]

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Describe your changes

Refactors ram_init_final.rs to replace hardcoded byte indices [0], [1], [2], [3] with helper functions using WORD_SIZE/WORD_SIZE_HALVED constants.

Changes:

• Added bytes_to_word_halves() helper function for evaluation context

• Added bytes_to_word_halves_packed() for optimized trace generation

• Replaced hardcoded indices in 4 functions: constrain_add_initial_values, constrain_subtract_final_values, add_initial_values, subtract_final_values

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[letmehateu]

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[letmehateu]

recheck

[slumber]

Thank you for the PR. This code mirrors the memory checking component.