Start on insurance fund implementation

[Kay-Zee]

Closes: #84

Description

Implementation of insurance fund

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[vishalchangrani]

Tracked by Issue: #84

[mts1715]

More clearly:
creditRate = debitRate * (totalDebitBalance / totalCreditBalance) - insuranceRate

[jordanschalm]

This transaction hard-codes a MOET-typed source for swapped funds but allows specifying a different output type for the created Swapper. I think we should:

• change the file name and documentation to reflect that this will always swap to MOET
• remove the swapperOutTypeIdentifier parameter and hard-code it to MOET

[UlyanaAndrukhiv]

I intentionally kept swapperOutTypeIdentifier configurable in this test transaction so we can explicitly test the validation logic in setInsuranceSwapper.

In particular, this allows us to verify that the function correctly rejects invalid swappers and triggers the expected error:
Swapper output type must be MOET. If the transaction hard-codes the output type to MOET, these failure paths would no longer be testable via transactions.

I also updated the documentation (942a305) for cadence/tests/transactions/flow-credit-market/pool-governance/set_insurance_swapper_mock.cdc to clarify that this flexibility is intended for test-only use.
For production usage, there is a dedicated transaction at:
cadence/transactions/flow-credit-market/pool-governance/set_insurance_swapper.cdc

[jordanschalm]

Makes sense -- thanks for explaining + adding that to the docs

[jordanschalm]

Reviewed the diff since my last review. Looks good besides the coverage file.

[UlyanaAndrukhiv]

@Gornutz, @liobrasil, since you’ve already reviewed this PR, would you mind taking a final look so we could merge it? Thanks!