The 'shape' argument of 'numpy.ndarray's initialization method accepts
integer and sequences of integers. But the 'shape' property of
'numpy.ndarray' always returns tuple[int, ...], so numpy manually
casts any legal argument into tuple[int, ...].

In 'BigArray' and 'ZBigArray' this internal casting didn't exist yet.
This patch adds the casting.

Before:

  ZBigArray(shape=[1, 2, 3], dtype=float).shape == [1, 2, 3]

After:

  ZBigArray(shape=[1, 2, 3], dtype=float).shape == (1, 2, 3)

In this way BigArray and ZBigArray API behaves closer to numpy.ndaray,
which should help avoiding confusion when people are using BigArray /
ZBigArray.

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See issue nexedi/wendelin.core#9 and
MR nexedi/wendelin.core!14
for additional context.

/reviewed-by @kirr
/reviewed-on nexedi/wendelin.core!14