test: improve code coverage for CLI tools and RangeShardStrategy

- Add 19 tests for CLI tools (MigrationGenerator, ModelGenerator, SchemaInspector, BaseCliCommand)
- Add 19 tests for RangeShardStrategy covering all edge cases
- Improve MigrationGenerator coverage: 0% → 33.33% methods, 44.07% → 81.36% lines
- Improve ModelGenerator coverage: 12.50% → 37.50% methods, 56.48% → 70.37% lines
- Improve BaseCliCommand coverage: 36.36% → 54.55% methods, 25.89% → 27.68% lines
- Improve RangeShardStrategy coverage: 33.33% → 100% methods, 87.10% → 100% lines

All 2242 tests passing with 7550 assertions.

Author: tommyknocker