- Remove chainfire_client.txn() calls (method doesn't exist)
- Use compare_and_swap(key, 0, value) for atomic wallet creation
- Use put() for wallet updates (CAS on version deferred to later)
- Remove unused proto imports (TxnRequest, TxnResponse, etc.)
- Simplify error handling using CasOutcome.success
This fixes compilation errors found in audit. CreditService now
compiles successfully.
Refs: Audit Fix 1/3
