fix(hex-primality): preserve next-prime search work accounting

[kim-em]

Closes #9799.

Summary

• split next-prime exhaustion accounting into conclusively rejected candidates and randomized certificate attempts
• retain the failing candidate's decision-attempt subtotal and exact advanced Rand state
• document failure-mode detection and resumption, and add focused guards for exhaustion and least-prime success across dispatch tiers

API note

• this intentionally replaces the ambiguous public NextPrimeFailure.attempts field with rejectedCandidates and certAttempts

Verification

• lake build HexPrimality HexConformance
• lake build HexPrimality HexPrimality.Conformance