Clear phantom debt/collateral types after exact zeroing

[liobrasil]

Summary

Fix phantom debt/collateral type retention after exact zeroing so one-type guardrails in PR #184 are released correctly when a type balance is fully cleared.

Previous behavior (bug example)

Example position lifecycle:

• Collateral: MOET
• Debt: FLOW

Action sequence:

1. Borrow 300 FLOW (debt type becomes FLOW).
2. Repay exactly 300 FLOW (debt balance reaches 0).
3. Try to borrow 100 MOET.

Before this fix:

• The debt-type list still included FLOW even at zero balance.
• validateDebtType treated position as still locked to FLOW debt.
• Borrowing MOET incorrectly failed due to a phantom/stale debt type.

Equivalent issue also existed for collateral:

• After exact full withdrawal of the only collateral token, the collateral-type list could still keep that token type at zero balance, incorrectly blocking a new collateral type deposit.

Why this fix is needed

PR #184 intentionally adds temporary one-collateral/one-debt constraints. Those constraints must track active non-zero balances, not stale zero balances. Otherwise users can get permanently constrained by phantom types after valid exact repay/withdraw flows.

What changed

• Updated type list helpers in FlowALPModels.cdc:
  • getDebtTypes() now includes only types with scaledBalance > 0.0.
  • getCollateralTypes() now includes only types with scaledBalance > 0.0.
• This ensures type constraints reflect real active exposure and clear automatically after exact zeroing.

Tests

• Added regression tests in cadence/tests/debt_type_constraint_three_token_test.cdc:
  • testExactRepayClearsDebtTypeConstraint
  • testExactFullWithdrawClearsCollateralTypeConstraint
• Ran:
  • flow test cadence/tests/debt_type_constraint_three_token_test.cdc
  • flow test cadence/tests/single_token_constraint_test.cdc