fix: streaming subscription enum type mismatch + correct field maps

[rdemeritt]

Root cause

_send_subscription built fields from EQUITY_FIELD_MAP.keys() — plain ints. schwab-py's StreamClient requires LevelOneEquityFields / LevelOneOptionFields enum members and raises on type mismatch:

expected type "LevelOneEquityFields", got type "int". (initialize with enforce_enums=False to disable this checking)

Fix

• Convert field keys to enum members at subscription time:

  fields = [sc.LevelOneEquityFields(k) for k in EQUITY_FIELD_MAP]
  fields = [sc.LevelOneOptionFields(k) for k in OPTIONS_FIELD_MAP]

• Corrected both field maps: previous names were wrong (e.g. key 10 was labeled tradeTime but is HIGH_PRICE; keys 19-23 on options were mislabeled as greeks but are metadata fields)
• Updated field selection to a sensible set for a quote proxy: bid/ask/last/size, OHLC, volume, mark, net change, timestamps; options add greeks (delta/gamma/theta/vega/rho), days-to-expiry, underlying price

Validated

All 44 field integer keys confirmed against LevelOneEquityFields and LevelOneOptionFields enums in schwab-py 1.5.1. 19/19 tests pass.