chore: release v5.2.0

[hogan-yuan]

Release v5.2.0. Bumps workspace 5.1.0 → 5.2.0.

New since v5.1.0

• Breaking: TradeContext.fund_positions — the FundPosition identifier field is renamed symbol → counter_id across all layers (C lb_fund_position_t.counter_id, C++ FundPosition::counter_id, Java getCounterId(), Node.js counterId, Python counter_id). The value is now the full fund counter_id (e.g. UT/FD/HK0000384492); the ISIN is recoverable as its last /-separated segment. Rust keeps a symbol serde alias for transition; the request-side filter GetFundPositionsOptions.symbols is unchanged (feat(fund): add FundContext for the mutual-fund channel (all layers) #598)
• Added: mutual-fund channel FundContext / FundContextSync — 28 endpoints across fund catalog & market data, the user's fund positions, and fund orders/trading. Funds are addressed by counter_id (sent as a query parameter; the nav / performance / position_performance batch endpoints use a one-element counter_ids JSON array). Mirrored across C, C++, Java, Node.js and Python (the Go SDK ships separately, openapi-go#124) (feat(fund): add FundContext for the mutual-fund channel (all layers) #598)
• Changed: CalendarContext.finance_calendar now exposes pagination — count / offset / next (with the new CalendarPageDirection enum) (fix(calendar): expose finance_calendar pagination parameters #597)
• Fixed: C/C++ — resolved a cbindgen name collision from the fund FFI: CFundPosition / CGetFundPositionsOptions were renamed to CFundPositionItem (lb_fund_position_item_t) / CFundPositionsOptions (lb_fund_positions_options_t) so they no longer overwrite the portfolio types (feat(fund): add FundContext for the mutual-fund channel (all layers) #598)

#598 is technically breaking; released as minor per maintainer decision.