feat: arbiter panel repetition guard for a supplier consecutive disputes

[shakurJJ]

Summary

Arbiter assignment for a dispute doesn't consider whether the same arbiter (or panel) already ruled on a prior dispute for the same supplier. This proposes a repetition guard so a supplier doesn't repeatedly face the same arbiter.

Proposed Behaviour

• Track the last N arbiters assigned to disputes for a given supplier.
• When assigning a panel for a new dispute, skip arbiters that appear in the supplier's recent-assignment history if an alternative from the pool is available.
• Falls back to allowing repetition if the pool is too small to satisfy the panel size without it.

Acceptance Criteria

• Recent arbiter history is tracked per supplier
• Panel assignment avoids recent arbiters when the pool allows it
• Falls back gracefully when the pool is too small
• Tests cover both paths

[Thomson-dev]

@Thomson-dev has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

pls can work I on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Thomson-dev to this issue.