Fix ctypes memory safety and enrich tests

[chkwon]

Summary

• Plug a C-side memory leak. delete_solution was only called on the happy path. If RoutingSolution extraction raised mid-construction, the C-allocated Solution (plus every route's path buffer) leaked. Wrapped the extraction in try/finally.
• Stop relying on undocumented numpy behavior for buffer lifetime. The old arr.astype(c_double).ctypes + cast(...) idiom never bound the temporary ndarray to a local — it survived only via numpy's _ctypes proxy back-reference. Replaced with named np.ascontiguousarray(arr, dtype=np.float64) locals + .ctypes.data_as(c_double_p), which pins the buffer through the C call and removes up to two redundant n² copies of the distance matrix (the old code did reshape followed by an always-copying astype).
• Enrich the test suite (5 → 15 tests). Added regressions for the two fixes, dtype/contiguity variants (float32, non-C-contiguous dist_mtx, int demands, list coords), input-validation assertions, solver reuse, and CVRP solution invariants (every customer visited exactly once, depot not in route bodies, capacity respected).
• Modernize CI Python matrix from ["3.11", "3.10"] to ["3.10", "3.13"].

Coverage on hygese/hygese.py is now 95% (8 missed lines are platform-specific branches like Windows-only and solve_tsp via coords).

Test plan

• pytest hygese/tests/ -v — all 15 tests pass locally on macOS / Python 3.13 (~16 s).
• pytest --cov=hygese hygese/tests/ — coverage on hygese/hygese.py at 95%, with the new try/finally and ascontiguousarray paths fully covered.
• Exception-path regression: test_delete_called_on_exception monkey-patches RoutingSolution.__init__ to raise and asserts delete_solution is still invoked exactly once.
• Zero-copy fast path: np.shares_memory(x, np.ascontiguousarray(x, dtype=np.float64)) is True when x is already float64/C-contiguous.
• CI green on ubuntu-latest / windows-2019 / macos-latest × Python 3.10 / 3.13.

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