feat: Phase 1 — real-time & historical data system

New data/ module with:
- data/store.py: Parquet-based raw message storage with background writer
  thread. Messages partitioned by channel/coin/date. Thread-safe queue.
  Supports pyarrow Parquet with zstd compression. Includes read_range()
  helper for replay.

- data/collectors/hyperliquid.py: HL WebSocket + REST collector
  - WebSocket: l2Book (full book reconstruction), trades, allMids (mark prices)
  - REST pollers: funding rates, predicted funding, open interest, liquidations
  - Per-coin OrderBook class with snapshot/update reconstruction
  - Sequence gap detection with per-coin re-snapshot on gap
  - Latency tracking (exchange transport, signal, order, roundtrip)
  - Periodic stats reporter (book stats + latency summary every 60s)
  - CLI entrypoint: python -m data.collectors.hyperliquid --coins BTC ETH

- data/normalizer.py: Timestamp normalization (ms, s, ISO strings from
  HL/Binance/Bybit/OKX/Coinbase/Deribit) + SequenceTracker with gap detection

- data/latency.py: Rolling-window latency metrics (p50/p90/p95/p99) for
  transport, signal computation, order submission, and roundtrip

- Added pyarrow + aiohttp to requirements.txt

data/collectors/__init__.py

@@ -0,0 +1,5 @@
+"""
+Market data collectors.
+
+hyperliquid.py — HL WebSocket (L2 books, trades, marks) + REST pollers (funding, OI, liquidations)
+"""