feat(transaction-contract): Soroban transaction manager for issue #22

[titilayo967]

Pull Request: Implement Comprehensive Transaction Management Contract

Implements the full Transaction Management smart contract as outlined in #22.

Changes

Core Modules:

• execution_engine: Atomic multi-operation execution with rollback
• state_machine: Transaction lifecycle management (Draft → Pending → Executing → Completed/Failed)
• dependency_resolver: Operation ordering and parallel execution
• gas_optimizer: Gas estimation, batch compression, and operation reordering
• signature_manager: Multi-sig collection and verification
• recovery_system: Transaction recovery and retry mechanisms

Security:

• Atomic execution guarantees with automatic rollback
• Pre-flight validation, permission checking, and resource guards
• Signature verification with threshold and time-lock support

Storage:

• Modular storage layer with transaction, operation, state, and cache stores
• Immutable audit trail with state persistence

Testing:

• Expanded test coverage for execution paths, dependency failures, and recovery scenarios

Files

32 files changed, 1361 insertions(+), 103 deletions(-)

Key Additions

Module	Purpose
execution_engine.rs	Atomic execution with rollback
state_machine.rs	State transitions and validation
signature_manager.rs	Multi-sig collection
security/	Validation, permissions, resource limits
storage/	Transaction and state persistence
utils/	Gas calc, param encoding, error handling

Closes #22

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[titilayo967]

@Oluwaseyi89 please, review now.