UnifiedApi (UTA v3): history-strategy-orders fails to deserialize (cursor is a number) + a few serialization/missing-parameter issues #111

Hi, thanks for the library. While migrating a futures bot from the Classic V2 API to the Unified Account (V3) API with JK.Bitget.Net 4.5.0 (.NET Framework 4.7.2 and .NET 10) I ran into the following. Item 1 is a hard bug, the rest are smaller issues / missing pieces.

1. UnifiedApi.Trading.GetClosedStrategyOrdersAsync — deserialization error (bug)

GET /api/v3/trade/history-strategy-orders returns data.cursor as a JSON number, but BitgetUaStrategyOrders.Cursor is declared as string?, so every call fails as soon as the account has at least one historical strategy order:

Json deserialization failed: The JSON value could not be converted to System.String.
Path: $.data.cursor | LineNumber: 0 | BytePositionInLine: 694

Suggested fix: read cursor with a number-or-string converter (same for other UTA paging models if Bitget does the same there).

2. UnifiedApi.Trading.PlaceStrategyOrderAsync — two parameters serialized in V2 format

• reduceOnly is added with BoolSerialization.String → sends "true"/"false". The V3 doc for place-strategy-order expects "yes"/"no" (the regular PlaceOrderAsync already sends yes/no correctly).
• triggerBy, tpTriggerBy, slTriggerBy are typed as Enums.V2.TriggerPriceType, which maps to fill_price / mark_price. The V3 endpoint expects market / mark.

Workaround today: omit these parameters (only possible in hedge mode with the default trigger source).

3. UnifiedApi.Account.SetLeverageAsync — missing parameters

The method only has leverage and positionSide. POST /api/v3/account/set-leverage also accepts marginMode, longLeverage, shortLeverage. In hedge mode + isolated margin the API rejects the request without them:

25200: ... DOUBLE_SIDE_HOLD afterShortLeverage and afterLongLeverage none

Related: BitgetUaAccountInfoSymbol (GetAccountConfigAsync -> symbolConfigList) only maps category, symbol, marginMode, leverage. The API also returns longLeverage and shortLeverage per symbol, which are the values that matter in hedge mode + isolated margin (currently only readable from OriginalData).

4. Missing endpoints / parameters (would be nice to have)

• POST /api/v3/account/set-margin (add / remove isolated position margin)
• POST /api/v3/account/upgrade and GET /api/v3/account/upgrade-status (switch Classic → Unified)
• GET /api/v3/trade/strategy-sub-orders (child orders of a triggered strategy order)
• GET /api/v3/account/funding-financial-records
• GetClosedOrdersAsync: the API has a symbol filter, the method has no such parameter
• ProductCategory has no OTHER value, which GET /api/v3/account/financial-records accepts as category

5. Minor

• GetPositionsAsync returns Success = true with Data = null when the account has no positions (API sends "list": null); an empty array would be easier to consume.

Happy to test a pre-release build. Thanks!