feat: Add comprehensive tests for CrossChainBridge functionality

[ayinde38]

• Add cross-chain bridge contract for Stellar ↔ EVM asset transfers

• Lock-and-mint / burn-and-release model with relayer authorization
• Support for Ethereum and Polygon chains
• Inbound flow: relayers claim locked tokens and mint on Stellar
• Outbound flow: users lock tokens on Stellar for EVM minting
• Timeout-based refunds for stuck outbound transfers (~7 days)
• Reentrancy guard and nonce replay protection
• Emergency pause capability for circuit breaker functionality
• Per-transfer min/max amount limits and chain allowlist
• Comprehensive test coverage for all flows and edge cases

• Add escrow contract for secure multi-party transactions
• Update workspace Cargo.toml to include new bridge and escrow contracts
• Update Cargo.lock with new contract dependencies
• Enhance reputation score contract with additional test coverage
• Implement checks-effects-interactions pattern throughout for security

Closes: #154
Closes: #155

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