Multiple Collateral Types & Cross-Asset Operations Testing

[UlyanaAndrukhiv]

Closes: #148

Description

Adds comprehensive test coverage for positions using multiple collateral types and cross-asset borrowing.

Tests added (fork_multi_collateral_position_test.cdc)

• test_multi_collateral_position — FLOW + USDF + WETH collateral; weighted health calculation and max borrow capacity
• test_cross_asset_flow_to_usdf_borrowing — deposit FLOW, borrow USDF
• test_cross_asset_flow_usdf_weth_borrowing — FLOW → USDF → WETH chain; netting when borrowing same token held as collateral
• test_cross_asset_chain — four-asset path FLOW → USDF → WETH → WBTC, intermediate assets net to zero
• test_multi_asset_uncorrelated_price_movements — FLOWprice +10%, USDF price -5%, WETH price +20% simultaneously
• test_multi_asset_partial_withdrawal — partial withdrawal from multi-asset position; verifies remaining balances
• test_cross_collateral_borrowing_capacity — borrowing same token as collateral caps at credit amount; different token uses health-based formula
• test_multi_asset_liquidation_collateral_selection — 3 collateral types + 2 debt types; liquidator selects which collateral to seize
• test_multi_asset_complex_workflow — full lifecycle with price change and auto-rebalance; verifies exact MOET pushed to drawDownSink and health restored to target health

Refactoring

• Added manualLiquidation, setupGenericVault, transferFungibleTokens and updated createPosition, borrowFromPosition test helpers
• Moved create_and_store_pool.cdc to tests/transactions/ folder cause pool setup depends on both mocks