Parallel Soroban testing

[sisuresh]

• Run code coverage and add tests for missing branches
• Apply load test with classic payments, SAC payments, and contract data entry updates. Make sure to test that ledger hashes are stable with repeated runs.
• understand and eliminate (or inhibit) all differences detected through synthetic parallel pre-exec framework running on mainnet
• Apply load tests and mainnet pre-exec with asan, tsan, ubsan
• Check that latency, throughput and memory metrics are within expectations on mainnet and loadgen
• See if it's possible to use the static thread checking annotations to describe the parallel execution system