HookSwap URC Defines Canonical Accounting Event for Uniswap v4

**HookSwap URC proposed for Uniswap v4 custom-accounting hooks.** Defines a canonical event reporting token deltas from hook-specific swap logic, excluding AMM fields like sqrtPriceX96, liquidity, tick. Hooks MUST emit exactly one HookSwap per successful swap where they contribute a delta. Sign convention matches core v4, from swapper perspective. Enables accurate indexing when hooks alter swap accounting.