fix(data): parse combo trade activity

[cesarenaldi]

Summary

• Add public ComboTradeActivity for Data API TRADE rows with isCombo=true.
• Preserve existing CLOB TradeActivity behavior and route trade parsing on isCombo.
• Re-export ComboTradeActivity from the public package.

Linear

• DEV-270

Verification

• uv run pytest tests/unit/test_data_activity.py
• uv run ruff check .
• uv run pyright
• uv run pytest tests/unit

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Note

Low Risk
Additive parsing and model changes with explicit routing; existing CLOB TradeActivity paths are preserved and covered by tests.

Overview
Adds ComboTradeActivity so Data API TRADE payloads with isCombo: true parse into a dedicated type instead of failing or mis-typing combo rows as CLOB trades.

parse_activity now branches on type == "TRADE" and isCombo before the generic trade handler: combo trades use ComboConditionId and position_id (from asset), with a slimmer field set (no outcome/slug/event fields). TradeActivity gains an explicit is_combo: False default so non-combo trades stay unchanged.

ComboTradeActivity is re-exported from the public package; a unit test covers combo trade parsing.

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