Persist scoring window and voted swaps across validator restarts

[bitloi]

Closes #16

Summary

• Add ScoringWindowStore for atomic JSON persistence of the scoring window and voted set, following the existing tmp-file-then-rename pattern used by SwapFulfiller._save_sent_cache.
• Wire persistence into SwapTracker load on initialize(), persist on swap resolution, window pruning, and mark_voted().
• Remove duplicate _resolved_block helper by sharing a single resolved_block() from the store module.
• Create store in validator init with cache path at <neuron.full_path>/scoring_window.json.

Design

Persistence hooks at every state mutation point only. The store is optional (None disables persistence) so existing tests and standalone usage remain unaffected. On cold start, stale voted IDs are pruned against the active swap set to prevent unbounded growth.

Test plan

• ruff check allways/validator/scoring_store.py allways/validator/swap_tracker.py neurons/validator.py passes
• python3 -m pytest tests/test_rate.py tests/test_chains.py -q --tb=short passes
• python3 -m pytest tests/test_scoring_store.py -q --tb=short passes (local)
• Roundtrip serialization preserves window and voted IDs
• Corrupt/missing cache file falls back to empty state
• Stale voted IDs pruned on restart when no active swaps exist
• Window entries older than SCORING_WINDOW_BLOCKS pruned on load

[bitloi]

@LandynDev @anderdc Ready for review!