Add SDK transaction simulation result mapper

[panditdhamdhere]

Summary

• Implements mapSimulationResult to classify Soroban simulateTransaction responses as success | warning | failed | unsupported | unknown
• Wires ContractClient (readOnly / invoke / auth sim) and simulateContractCall through the mapper before assemble/sign
• Adds typed error codes (SOROBAN_SIMULATION_FAILED / _UNSUPPORTED / _UNKNOWN), fixtures, tests, and docs

Closes #337

Acceptance criteria

• Simulation result mapper is implemented
• Success, warning, failed, unsupported, and unknown states are represented
• Soroban client uses the mapper
• Tests cover representative simulation responses
• Errors are typed and safe
• Documentation explains simulation handling

Test plan

• npx vitest run tests/simulation-mapper.test.ts tests/contract-client-factory.test.ts
• Confirm invoke returns simulation_error and does not sign on failed/unsupported
• Confirm docs/simulation-result-mapping.md matches behaviour