#81 — Add ADL full-close test

[IbrahimIjai]

• Priority: P1 | Size: M | Requires: #77 — Implement ADL state update function #79
• Description: Verify ADL can fully close a target position.
• Files: contracts/adl_handler/src/lib.rs, contracts/order_handler/src/lib.rs, libs/decrease_position_utils/src/lib.rs.
• Done: Position key is removed. OI returns to pre-position baseline. Pool PnL factor reflects the full close.

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Source: issues_v2.md, issue #81.