Contract Load Testing Harness

[Luluameh]

Background
We need to understand how the contract behaves under load (1000+ concurrent sessions) before mainnet launch.
Goal
Build a load testing script that simulates a high volume of start_session, settle_session, and end_session calls against a local Soroban sandbox.
Acceptance Criteria

• Script in scripts/load_test.sh or scripts/load_test.ts.
• Configurable concurrency (N sessions) and duration.
• Outputs: average gas cost, p95 latency, and error rate.
• At least 500 sessions completed without errors in the CI baseline run.
  Key Files
  scripts/load_test.sh, `.github/workflows/load_test.yml