refactor(array): share one immutable ArrayState between Array and AsyncArray

Array and AsyncArray now hold the same `_StateCell`, a single mutable slot
containing a frozen `ArrayState` (store path, metadata, runtime config, chunk
grid, codec pipeline). Members that are derived from that state without IO are
defined once on a shared `_ArrayBase`. `Array` does its own IO through the
module-level functions instead of calling through its `AsyncArray`, which is
kept only as the handle returned by `async_array`.

resize, append and update_attributes are split into pure plan functions and a
short IO step that swaps the cell's state, replacing in-place mutation of a
frozen dataclass via `object.__setattr__` and of the attributes dict.

Assisted-by: ClaudeCode:claude-opus-5-5

Author: d-v-b