[CONTRACT] Implement performance optimizations for bulk shipment operations

[dinahmaccodes]

Tier: 🔴 Hard

Description:

Optimize contract performance for bulk operations including batched shipment creation, status updates, and escrow processing. Focus on reducing CPU/storage costs while maintaining correctness and safety guarantees.

Tasks:

• Profile current batch operation costs
• Implement index/caching optimizations
• Add lazy evaluation for non-critical operations
• Optimize storage access patterns
• Create performance benchmark suite

File locations:

• Optimizations in lib.rs → batch functions
• New benchmarks → benches/shipment_operations.rs
• Tests → tests/test_performance.rs

Acceptance Criteria:

• Batch operations run faster (measured benchmarks)
• Storage costs reduced (verify with budget checks)
• Correctness maintained (all tests pass)
• No unsafe code introduced
• Benchmarks documented

PR Checklist:

• Performance improvements measured
• Benchmarks showing improvement
• All tests still passing
• cargo test shows 100% pass rate
• No clippy warnings
• WASM size not increased significantly

Reference: Read CONTRIBUTING.md before starting.