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

[OlivierBBB]

Note

Adds EIP-7823 constants, enforces 1024-byte bound in MODEXP xbs, and rewrites Osaka MODEXP pricing with a 500 gas minimum; minor renames for comparison signals across forks.

• EIP-7823 support:
  • Add GAS_CONST_MODEXP_EIP_7823 (500) and EIP_7823_MODEXP_UPPER_BYTE_SIZE_BOUND (1024) in constants/constants.lisp.
• MODEXP xbs:
  • Osaka: implement upper-bound check against 1024, add xbs-within-bounds/xbs-out-of-bounds flags, enforce binarity, and expand hub-justification logic.
  • Cancun/London/Shanghai/Prague: rename prc-modexp-xbs---compo-to_512 to prc-modexp-xbs---comparison-to-512 and update constraints.
• MODEXP pricing (Osaka):
  • Replace prior logic with stepwise computation: checks for r@c and exponent-log isZero, computes ceil(max(mbs,bbs)/8) and derived raw-cost, compares against GAS_CONST_MODEXP_EIP_7823 (min 500), and validates callee-gas vs precompile cost.
• MODEXP lead (Osaka):
  • Rename comparison accessor to prc-modexp-lead---result-of-comparison and update usage.

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