feat: Add UInt256 precision improvements to DeFiBlocks

[nialexsan]

• Add DFBMathUtils contract for high-precision math operations
• Create DFBv2 with AutoBalancerV2 using UInt256 calculations
• Add AutoBalancerV2Adapter with utility functions
• Include comprehensive tests demonstrating precision improvements
• Add documentation explaining the improvements and migration guide

This follows the same pattern as TidalProtocol's precision upgrade, providing 18-decimal fixed-point arithmetic for better accuracy in DeFi calculations.

[sisyphusSmiling]

To be honest, I doubt the source of discrepancies originate from the AutoBalancer's decimal precision. Even after the precision refactor, the protocol pulls funds by UFix64 amounts, so IMO it's unlikely that the lack of precision here would cause errors. Particularly because all values related to the AutoBalancer - contained balances, prices, time, thresholds are all UFix64.

Additionally, I would really hope that Sourceconnectors integrating with TidalProtocol don't need to manage balances via UInt256 as that's quite a dev ex hurdly given Cadence-native tokens us UFix64.

That said, I think we should integrate this branch as a last resort after pulling latest from onflow/FlowALP#31 into the end-to-end test scenarios.

[nialexsan]

merged another change #14