Tabmat

-------------------

**Bug fixes:**

- We fixed a bug in the dense sandwich product, which would previously segfault for very large matrices.
- Fixed the column order when initializing a ``SplitMatrix`` from a list containing other ``SplitMatrix`` objects.
- Fixed ``getcol`` not respecting the ``drop_first`` attribute of a ``CategoricalMatrix``.

------------------

**Other changes:**

- Support building on architectures that are unsupported by xsimd.

------------------

**Other changes:**

- The C++ types have been refactored. Loop indices are now using the ``Py_ssize_t`` type. Integers now have a templated type as well.
- The documentation for ``matvec`` and ``matvec_transpose`` has been updated to reflect actual behavior.
- Checks for dimension mismatch in ``matvec`` and ``matvec_transpose`` arguments have been added.
- Remove upper pin on xsimd.

------------------

**Bug fix:**

- We fixed a bug in the cross sandwich product, which would previously segfault for very large matrices.

------------------

**Bug fix:**

- We fixed a bug in the dense sandwich product, which would previously segfault for very large F-contiguous matrices.

------------------

**Bug fix:**

- We fixed a bug in the dense matrix-vector and sandwich products, which would previously segfault for very large matrices.