Release v1.8.10

• orderbook.walk over a structured series (strikes, weather buckets) skips a market whose history is not built yet instead of raising ExportNotReadyError for the whole walk. Open markets have no history file, so a window that still held one (every weekly strike event until it resolves) used to fail; the backtest engine already skipped them. A single market walk still raises.
• README and examples: windows sized to a small share of the free allowance, the sports block dropped from the general examples, examples/event_strikes.py walks btc-multi-strikes-weekly.