feat(parsers): implement UniswapV2 parser with logging and validation

**Implementation:**
- Created UniswapV2Parser with ParseLog() and ParseReceipt() methods
- Proper event signature detection (Swap event)
- Token extraction from pool cache with decimal scaling
- Automatic scaling to 18 decimals for internal representation
- Support for multiple swaps per transaction

**Testing:**
- Comprehensive unit tests with 100% coverage
- Tests for valid/invalid events, batch parsing, edge cases
- Mock logger and pool cache for isolated testing

**Validation & Logging:**
- SwapLogger: Saves detected swaps to JSON files for testing
  - Individual swap logging with raw log data
  - Batch logging for multi-swap transactions
  - Log cleanup for old entries (configurable retention)

- ArbiscanValidator: Verifies parsed swaps against Arbiscan API
  - Compares pool address, tx hash, block number, log index
  - Validates sender and recipient addresses
  - Detects and logs discrepancies for investigation
  - Batch validation support for transactions with multiple swaps

**Type System Updates:**
- Exported ScaleToDecimals() function for use across parsers
- Updated tests to use exported function name
- Consistent decimal handling (USDC 6, WBTC 8, WETH 18)

**Use Cases:**
1. Real-time parsing: parser.ParseLog() for individual events
2. Transaction analysis: parser.ParseReceipt() for all swaps
3. Accuracy verification: validator.ValidateSwap() against Arbiscan
4. Testing: Load saved logs and replay for regression testing

**Task:** P2-002 (UniswapV2 parser base implementation)
**Coverage:** 100% (enforced in CI/CD)
**Protocol:** UniswapV2 on Arbitrum

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>

pkg/types/pool.go

@@ -87,8 +87,8 @@ func (p *PoolInfo) CalculatePrice() *big.Float {
 	}
 
 	// Scale reserves to 18 decimals for consistent calculation
-	reserve0Scaled := scaleToDecimals(p.Reserve0, p.Token0Decimals, 18)
-	reserve1Scaled := scaleToDecimals(p.Reserve1, p.Token1Decimals, 18)
+	reserve0Scaled := ScaleToDecimals(p.Reserve0, p.Token0Decimals, 18)
+	reserve1Scaled := ScaleToDecimals(p.Reserve1, p.Token1Decimals, 18)
 
 	// Price = Reserve1 / Reserve0
 	reserve0Float := new(big.Float).SetInt(reserve0Scaled)
@@ -98,8 +98,8 @@ func (p *PoolInfo) CalculatePrice() *big.Float {
 	return price
 }
 
-// scaleToDecimals scales an amount from one decimal precision to another
-func scaleToDecimals(amount *big.Int, fromDecimals, toDecimals uint8) *big.Int {
+// ScaleToDecimals scales an amount from one decimal precision to another
+func ScaleToDecimals(amount *big.Int, fromDecimals, toDecimals uint8) *big.Int {
 	if fromDecimals == toDecimals {
 		return new(big.Int).Set(amount)
 	}