Add gas usage optimization benchmarks for critical paths

[abayomicornelius]

Problem

No systematic tracking of instruction costs. Soroban has resource limits that could be hit.

Why it matters

Hitting instruction limits would cause transaction failures in production.

Suggested fix

Add benchmark suite measuring instruction costs for: execute_order, liquidate_position, execute_deposit.

Acceptance criteria

• Set up benchmark harness
• Measure critical path costs
• Set maximum thresholds
• CI fails if thresholds exceeded

[Rayyanah0]

Hello maintainer, i will like to work on this issue