bigarray: Add ArrayRef utility
ArrayRef is a tool to find out for a NumPy array its top-level root parent and remember instructions how to recreate original array from the root. For example if root = arange(1E7) z = root[1000:2000] a = z[10:20] `ArrayRef(a)` will find out that the root array for `a` is `root` and that `a` occupies 1010:1020 bytes in it. The vice versa operation is also possible, for example given aref = ArrayRef(a) it is possible to restore original `a` from `aref`: a_ = aref.deref() assert array_equal(a_, a) the restoration works without copying by creating appropriate view of root. ArrayRef should work reliably for arrays of arbitrary dimensions, strides etc - even fancy arrays created via stride tricks such as arrays whose elements overlap each other should be supported. This patch adds ArrayRef with support for regular ndarrays only. The next patch will add ArrayRef support for BigArray and description for ArrayRef rationale.
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