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

[OlivierBBB]

Note

Introduce explicit in-bounds signals and gate OOB/EXP/MMU and pricing logic on them, while adjusting leading-word and log computations for MODEXP.

• hub/osaka/constraints/.../modexp/common.lisp:
  • Bounds signals:
    • Add bbs-within-bounds/bbs-out-of-bounds, ebs-within-bounds/ebs-out-of-bounds, mbs-within-bounds/mbs-out-of-bounds, and aggregate all-byte-sizes-are-in-bounds.
  • bbs/ebs/mbs analysis:
    • In mbs OOB instruction, replace constant 1 with bbs-within-bounds for max selection gate.
  • Leading-word analysis:
    • Replace flag sum constraint with explicit gates: EXP and MMU flags tied to load-lead; OOB flag tied to all-byte-sizes-are-in-bounds; ensure MXP_FLAG and STP_FLAG are zero.
    • Gate setting of OOB/EXP/MMU instructions on their respective call flags.
    • Derive load-lead, cds-cutoff, ebs-cutoff, sub-ebs-32 from call-OOB-module-for-modexp-lead; compute raw-lead-* under call-MMU-module-for-modexp-lead.
    • Compute lead-log under call-EXP-module-for-modexp-lead; update modexp-full-log factor from 8 to 16.
  • Pricing analysis:
    • Gate OOB misc flag weight by all-byte-sizes-are-in-bounds.

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