Add unit tests for wallet search functionality

Test coverage for:
- Multi-word search with space delimiter (AND logic)
- startsWith matching for currencyCode, displayName, assetDisplayName
- includes matching for chainDisplayName, wallet name, contractAddress
- assetDisplayName and chainDisplayName only searched for mainnet assets
- Regression tests for original issues (#1: 'base eth', #3: 'eth' vs Tether)

Author: Jon-edge