Modernize the two-phase solver

[tcbegley]

Summary

• migrate the project to a uv/uv_build src layout with Ruff and ty tooling
• replace the mutable model and basic coordinates with immutable coordinate, symmetry, move, and pruning-table implementations
• add the symmetry-aware two-phase solver plus facelet parsing and formatted public helpers
• port the complete test suite in a dedicated commit

Validation

• just lint
• uv run pytest (437 passed)
• uv build

Benchmark notes

The new implementation is slower for trivial warm solves but solves a harder scramble in 0.67s where the previous implementation exceeded a 30s limit. Table generation is intentionally more expensive because it builds the added symmetry and transition tables; tables are persisted and cached in CI.