CustomData backtesting issues and improve docs

[graceyangfan]

Bug Report

CustomData can not be send to data engine properly

Expected Behavior

CustomDatd should be send to data engine properly

Specifications

OS platform: ubutnu24.04
Python version: python 3.12
nautilus_trader version:latest develop

how to fix this bug

from nautilus_trader.model.data cimport CustomData need to be add in nautilus_trader/data/engine.pyx

Backtest Setting Document

take GreekData as example at least setting is needed:

register_arrow(GreeksData, GreeksData.schema(), GreeksData.to_catalog, GreeksData.from_catalog)
BacktestDataConfig(
    catalog_path=str(catalog_path),
    data_cls=GreeksData.fully_qualified_name(),
    instrument_id=InstrumentId.from_str(instrument_id),
    start_time=start_time,
    end_time=end_time,
    client_id=client_id,
    metadata={"instrument_id": instrument_id},
)