Arraykit

Added ``BlockIndex.iter_contiguous()`` with options for ``ascending`` and ``reduce`` sequences.

Added ``slice_to_ascending_slice()``.

Updated ``BlockIndex.shape`` to internally cache the shape tuple.

Corrected ``BlockIndex.iter_select()`` handling of negative integers in sequences.

Updated ``BlockIndex.register()`` to handle 0-column 2D arrays and return False.

Added ``BlockIndex.rows``, ``BlockIndex.columns`` properties.

Updated unset ``BlockIndex.dtype`` to return a float dtype.

Added ``BlockIndex``, a tool to be used by ``TypeBlocks`` for mapping realized column positions to arrays.

Corrected potential issue in ``AK_CPL_resize_buffer`` that could segfault for very large offsets.

Simplified identification of ``pd.NaTType`` in ``isna_element()``.

Corrected potential memory leak in ``isna_element()``.