Add comprehensive tests for incremental index restore

This commit adds 5 comprehensive test cases covering all aspects of
incremental restore for global indexes:

1. BasicIndexIncrementalRestore:
   - Tests single global index restore
   - Verifies index functionality after restore
   - Tests querying via index after restoration

2. MultipleIndexesIncrementalRestore:
   - Tests table with 3 global indexes
   - Verifies all indexes restore correctly
   - Validates parallel index restore functionality

3. IndexDataVerificationIncrementalRestore:
   - Multi-shard table with index
   - Tests INSERT, UPDATE, DELETE operations across shards
   - Verifies index data integrity after restore
   - Compares before/after restore index query results

4. MultipleIncrementalBackupsWithIndexes:
   - Tests sequence of 3 incremental backups
   - Each backup has different operations (add, update, delete)
   - Verifies indexes restored correctly across all increments

5. MultipleTablesWithIndexesIncrementalRestore:
   - Tests backup collection with 2 tables
   - Each table has different global index
   - Verifies parallel restore of multiple table+index combinations

Test Coverage:
- Basic index restore ✓
- Multiple indexes per table ✓
- Multi-shard index tables ✓
- Index data verification ✓
- Multiple incremental sequences ✓
- Multiple tables with indexes ✓
- Parallel completion ✓ (implicitly tested in all tests)
- Index queries after restore ✓

Total: 506 lines of test code added

Author: claude