feat: fusdc liquidity pool borrow and repay facets

[0xpatrickdev]

refs: #10390

Description

• Adds borrower and repayer facets to the Liquidity Pool
• Track outstandingLends: Amount in state for checkPoolBalance invariant
• Track PoolMetrics like cumulative borrows, repays, and fees

Security Considerations

Handles payment allocations, but is able to do so synchronously using a temporary seats provided by the callers.

Scaling Considerations

Makes a vstorage writes for each borrow and repay.

Documentation Considerations

Updates code comments for maintainers.

Testing Considerations

Tests use test-only methods on the createFacet to simulate fees from a borrow/repay sequence. Tests ensure zcf.atomicRearrange() in .borrow() and .repay() will not fail and trigger zcf.shutdownWithFailure().

Upgrade Considerations

None, unreleased

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