fix(multicall): resolve critical multicall parsing corruption issues

- Added comprehensive bounds checking to prevent buffer overruns in multicall parsing
- Implemented graduated validation system (Strict/Moderate/Permissive) to reduce false positives
- Added LRU caching system for address validation with 10-minute TTL
- Enhanced ABI decoder with missing Universal Router and Arbitrum-specific DEX signatures
- Fixed duplicate function declarations and import conflicts across multiple files
- Added error recovery mechanisms with multiple fallback strategies
- Updated tests to handle new validation behavior for suspicious addresses
- Fixed parser test expectations for improved validation system
- Applied gofmt formatting fixes to ensure code style compliance
- Fixed mutex copying issues in monitoring package by introducing MetricsSnapshot
- Resolved critical security vulnerabilities in heuristic address extraction
- Progress: Updated TODO audit from 10% to 35% complete

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pkg/contracts/executor.go

@@ -11,6 +11,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	etypes "github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/ethclient"
+
 	"github.com/fraktal/mev-beta/bindings/arbitrage"
 	"github.com/fraktal/mev-beta/bindings/flashswap"
 	"github.com/fraktal/mev-beta/bindings/interfaces"
@@ -358,10 +359,17 @@ func (ce *ContractExecutor) prepareTransactionOpts(ctx context.Context) (*bind.T
 		return nil, fmt.Errorf("failed to get account nonce: %w", err)
 	}
 
+	// Check nonce safely before creating transaction options
+	nonceInt64, err := security.SafeUint64ToInt64(nonce)
+	if err != nil {
+		ce.logger.Error("Nonce exceeds int64 maximum", "nonce", nonce, "error", err)
+		return nil, fmt.Errorf("nonce value exceeds maximum: %w", err)
+	}
+
 	// Create transaction options
 	opts := &bind.TransactOpts{
 		From:     ce.accountAddress,
-		Nonce:    big.NewInt(int64(nonce)),
+		Nonce:    big.NewInt(nonceInt64),
 		Signer:   ce.signTransaction, // Custom signer function
 		Value:    big.NewInt(0),      // No ETH value for arbitrage transactions
 		GasPrice: ce.gasPrice,