Databento integration

[cjdsellers]

Add an initial integration for Databento covering US equities, futures, options on futures and equity options.

• Data loader for Databento Binary Encoding (DBN) files
• Feeding backtest engines with decoded DBN -> Nautilus data
• Writing from decoded DBN -> Nautilus Parquet format with the data catalog
• Rust client library integration for historical requests & live data feeds

Still to go:

• [x] Write Databento integration guide
• [x] Improve the code and efficiency a little more (can always improve this)
• [x] Re-add support for MBP-10 (L2 order book data, top 10 levels aggregated snapshots)
• [x] Add support for imbalance and statistics schemas
• [x] Add support for continuous, parent and instrument_id symbology types
• [x] Test with more backtest and live examples
• [x] Fix continuous contract subscriptions
• [ ] Add some more test coverage generally
• [ ] Write how to setup a Databento data catalog guide
• [ ] Write some per asset class examples

[wayneadams]

Up voting for priority planning 🙏