You are a quantitative trader. Create a comprehensive guide to mean reversion trading in cryptocurrency. The guide must cover: 1) Mean reversion concepts (oversold/overbought, Bollinger Bands), 2) RSI and Stochastic oscillators, 3) Pairs trading and cointegration, 4) Statistical arbitrage approaches, 5) Entry and exit timing, 6) Risk management for mean reversion, 7) Market regime detection (trending vs ranging), 8) Backtesting mean reversion strategies, 9) Crypto-specific challenges (volatility, gaps), 10) Combining with other indicators. Provide Python code for backtesting.