fix(critical): eliminate uint256 max overflow by fixing signed int256 parsing across all event parsers

This commit resolves the uint256 max overflow causing amounts to display as +11579208923...

Root cause: UniswapV3 uses signed int256 for amounts, but multiple parsers treated them as unsigned

Files fixed:
- pkg/events/parser.go: Fixed broken signed int conversion (line 392-396)
- pkg/pools/discovery.go: Added signed parsing for UniswapV3 (lines 415-420, 705-710)

Impact: Eliminates e+59 to e+70 overflow values, enables accurate arbitrage calculations

pkg/events/parser.go

@@ -18,6 +18,27 @@ import (
 	"github.com/fraktal/mev-beta/pkg/uniswap"
 )
 
+// parseSignedInt256 correctly parses a signed 256-bit integer from 32 bytes
+// This is critical for UniswapV3 events which use int256 for amounts
+func parseSignedInt256(data []byte) *big.Int {
+	if len(data) != 32 {
+		return big.NewInt(0)
+	}
+
+	value := new(big.Int).SetBytes(data)
+
+	// Check if the value is negative (MSB set)
+	if len(data) > 0 && data[0]&0x80 != 0 {
+		// Convert from two's complement
+		// Subtract 2^256 to get the negative value
+		maxUint256 := new(big.Int)
+		maxUint256.Lsh(big.NewInt(1), 256)
+		value.Sub(value, maxUint256)
+	}
+
+	return value
+}
+
 // EventType represents the type of DEX event
 type EventType int
 
@@ -388,21 +409,13 @@ func (ep *EventParser) parseUniswapV3Swap(log *types.Log, blockNumber uint64, ti
 		return nil, fmt.Errorf("invalid Uniswap V3 Swap event log")
 	}
 
-	// Parse the data fields
-	amount0 := new(big.Int).SetBytes(log.Data[0:32])
-	amount1 := new(big.Int).SetBytes(log.Data[32:64])
+	// Parse the data fields - UniswapV3 uses signed int256 for amounts
+	amount0 := parseSignedInt256(log.Data[0:32])
+	amount1 := parseSignedInt256(log.Data[32:64])
 	sqrtPriceX96 := new(big.Int).SetBytes(log.Data[64:96])
 	liquidity := new(big.Int).SetBytes(log.Data[96:128])
 	tick := new(big.Int).SetBytes(log.Data[128:160])
 
-	// Convert to signed values if needed
-	if amount0.Cmp(big.NewInt(0)) > 0x7fffffffffffffff {
-		amount0 = amount0.Sub(amount0, new(big.Int).Lsh(big.NewInt(1), 256))
-	}
-	if amount1.Cmp(big.NewInt(0)) > 0x7fffffffffffffff {
-		amount1 = amount1.Sub(amount1, new(big.Int).Lsh(big.NewInt(1), 256))
-	}
-
 	event := &Event{
 		Type:            Swap,
 		Protocol:        "UniswapV3",