Pre-check key existence before delete to return accurate deleted count.
This unblocks integration tests while proper RaftResponse propagation
is deferred to T053.
- Single key: check exists via state_machine.kv().get()
- Range: count keys via state_machine.kv().range()
- Returns deleted=1 if key existed, deleted=0 otherwise
Integration tests now pass: 3/3 ✓
Refs: T059.S2 Option A (approved by PeerA)
- 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
