test(frontend): cover oisy trade canister wrappers

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Motivation

Recent OISY Trade wrapper changes added retry-aware Result handling across several read and certified write methods, but only getMyOrders had direct canister-wrapper coverage. These wrappers are core trading plumbing: a regression could silently drop arguments, return the wrong Ok payload, or lose retryability/reason metadata that callers use for recovery and UX.

Risky behavior now covered:

• Ok unwrapping for balances, deposits, withdrawals, order-book reads, and limit-order mutations.
• Argument forwarding for read wrappers and certified write wrappers.
• Retry-aware Err mapping for temporary and request failures, including fallback reason discriminants.

Changes

• Updated src/frontend/src/tests/lib/canisters/oisy-trade.canister.spec.ts with typed fixtures for trading pairs, balances, orders, requests, and responses.
• Added focused Vitest coverage for getBalances, deposit, withdraw, getOrderBookTicker, getOrderBookDepth, addLimitOrder, and cancelLimitOrder.
• Replaced the existing partial getMyOrders fixture with a concrete typed UserOrder fixture.

Why these tests materially reduce regression risk:

• They lock down the boundary between generated canister actors and frontend trading services, where small wrapper mistakes can affect deposits, withdrawals, and order execution flows.
• They verify both success and error disposition semantics without relying on live canisters or network calls.

Tests

• Passed: PATH="$HOME/.nvm/versions/node/v24.18.0/bin:$PATH" npx vitest run src/frontend/src/tests/lib/canisters/oisy-trade.canister.spec.ts (17 tests)
• Passed: PATH="$HOME/.nvm/versions/node/v24.18.0/bin:$PATH" npx prettier --check src/frontend/src/tests/lib/canisters/oisy-trade.canister.spec.ts
• Passed: PATH="$HOME/.nvm/versions/node/v24.18.0/bin:$PATH" npx eslint src/frontend/src/tests/lib/canisters/oisy-trade.canister.spec.ts
• Blocked by existing unrelated issue: npm run test -- src/frontend/src/tests/lib/canisters/oisy-trade.canister.spec.ts and npm run check:tests fail before running this spec because src/frontend/src/sol/utils/sol-instructions-system.utils.ts:96 passes SystemInstruction.CreateAccountAllowPrefund to assertNever.
• Blocked by existing unrelated formatting drift: full npm run lint -- --max-warnings 0 reports Prettier issues in 33 unrelated files; the updated spec passes targeted Prettier and ESLint.