test: add wallet creation SQLite lifecycle integration coverage

[j-kon]

Summary

• add a deterministic offline integration test for fresh SQLite wallet creation
• persist external and internal derivation state, dispose the original resources, and reload with a new persister
• verify network, zero balance, derivation indexes, and address scripts after reopening
• reuse the repository's retry cleanup pattern for cross-platform SQLite file handling

Closes #93

Why

Existing tests cover wallet constructors, loading a prebuilt SQLite fixture, and broad randomized or network-sync flows. This adds focused coverage for the create-to-persist-to-reload lifecycle against a previously nonexistent database.

Validation

• red check: without wallet.persist, reload restored derivation index 0 instead of the expected 1
• dart format --output=none --set-exit-if-changed lib test example
• dart analyze --fatal-infos --fatal-warnings lib test example
• dart test test/integration/wallet_creation_test.dart
• dart test (23 passed, 5 live-network tests skipped by their environment gate)