feat: implement blockchain indexing service (BE-003)

[Tobi-8]

Summary

Implement the Blockchain Indexing Service (BE-003) — a production-ready TypeScript
service that synchronises TruthBounty protocol events from the blockchain into the
backend, with fault tolerance, reorg handling, and idempotent processing.

• RPC Connectivity (ProviderManager): HTTP + optional WebSocket provider with
  automatic failover and reconnection strategies
• Historical Block Sync: batch-processes past blocks (configurable batch size),
  resumable via checkpoint persistence
• Live Event Listener: WebSocket block subscription with polling fallback,
  auto-recovery on connection failure
• Event Processing Pipeline (EventPipeline): fetches logs, parses via ethers.js
  Interface, deduplicates by tx hash + log index, enriches with block metadata
• Reorganisation Handling (detectReorg): verifies block hashes up to configurable
  depth (default 12 blocks), rolls back to fork point and replays
• Idempotent Processing: tracks transactionHash:logIndex per event, skips
  duplicates on retry or replay
• Indexing Checkpoints (CheckpointManager): persists blockNumber + blockHash
  after each sync batch, resumes from checkpoint on restart
• Storage Abstraction (StorageAdapter): InMemoryStorage implementation included;
  designed for PostgreSQL swap via the interface
• Event Definitions: full ABI fragments for TruthBountyWeighted (8 events),
  ReputationDecay (4 events), ReputationSnapshot (2 events)
• CLI Entry Point (index.ts): loads config from env vars, starts/stop indexer,
  graceful shutdown on SIGINT

Architecture

config -> ProviderManager (RPC/WS)
         |
         v
      EventPipeline.fetchLogs()
         |
         v
      EventPipeline.processLogs() -> dedup -> deserialize -> enrich
         |
         v
      StorageAdapter.saveEvents() + CheckpointManager.saveCheckpoint()
         |
         v
      EventHandlers (logging, webhooks, etc.)
         ^
         |
      detectReorg() on each new block

Testing

• 14 unit tests covering storage, checkpoint, pipeline, indexer, and events
• Uses vitest with mocked providers, independent from Hardhat suite

Notes

• BE-002 (PostgreSQL) not yet available; InMemoryStorage is the default adapter
• Batch size: 1000 blocks, confirmations: 6, poll: 5s

Closes DigiNodes/truthbounty-api#270

[Tobi-8]

hey i can't seem to link this pr with the issue number