feat: refactor e2e partition planning algorithm

- Implement comprehensive PartitionPlanner with 3-phase optimization
- Add actual vs preferred leader awareness to prevent unnecessary reassignments
- Introduce rack-aware replica selection with load balancing
- Add deterministic iteration for consistent planning results
- Enhance logging with clearer no-op vs optimization messages
- Replace basic test coverage with comprehensive 13-test suite
- Fix bug where ensureLeaderCoverage used preferred instead of actual leaders
- Add early-exit guard for perfect actual leader coverage scenarios
- Support edge cases: broker restarts, uneven leadership, rack diversity
- Maintain backward compatibility with existing EndToEndTopicConfig

Author: weeco