[scanner] Health-factor scanner: 3-bucket DashMap classification (healthy / near-liq / liquidatable)

[obchain]

Context

Per-block, the scanner recomputes health factors and bucket-sorts positions. Healthy positions can be sampled less often; near-liquidation positions need pre-computed transactions ready to fire; liquidatable positions trigger the executor pipeline. DashMap gives us lock-free concurrent writes across protocol/chain tasks.

Scope

• charon-scanner/src/scanner.rs with a HealthScanner struct
• Three DashMap<Address, Position> buckets: healthy, near-liquidation, liquidatable
• Configurable thresholds in [bot] section (e.g. liquidatable_threshold = 1.0, near_liquidation_threshold = 1.05)
• Runs on every newHead from the block listener
• Emits a per-block log line with counts per bucket
• Pushes liquidatable positions into a channel for the executor

Acceptance criteria

• dashmap added to workspace dependencies and charon-scanner
• Three-bucket classification works against mocked positions
• Thresholds read from config, not hardcoded
• Per-block log: INFO scanner: block=N healthy=X near_liq=Y liquidatable=Z
• No lock contention — DashMap used in place of Mutex<HashMap>

References

• PRD section 4c (Health Factor Scanner)

[obchain]

Superseded — 3-bucket HealthScanner shipped in feat/09-health-scanner.