EIP-7823: Set upper bounds for MODEXP --- MMU side

[OlivierBBB]

Note

Adds EIP-7823 MODEXP upper-byte-size bound and updates MODEXP MMU preprocessing to use it, increasing MODEXP micro row totals to 64.

• Constants:
  • Add EIP_7823_MODEXP_UPPER_BYTE_SIZE_BOUND = 1024 in constants/constants.lisp.
  • Increase NB_MICRO_ROWS_TOT_MODEXP_ZERO and NB_MICRO_ROWS_TOT_MODEXP_DATA to 64 in mmu/osaka/constants.lisp.
• MMU MODEXP_DATA (mmu/osaka/instructions/modexp_data.lisp):
  • Use EIP_7823_MODEXP_UPPER_BYTE_SIZE_BOUND for left-padding instead of hardcoded 512.
  • Set TOT to NB_MICRO_ROWS_TOT_MODEXP_DATA; compute TOTNT as NB_MICRO_ROWS_TOT_MODEXP_DATA - (TOTLZ + TOTRZ).
  • Minor renaming/clarification of preprocessing constraint headings.

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