Fixes #16539

The implicit 0-padding that is done to small entropy inputs to make them the
size of the internal pool conflicts with the spawn keys, which start with an
appended 0.

In order to maintain stream compatibility with unspawned `SeedSequence`s, we
explicitly 0-pad short inputs out to the pool size only if the spawn key is
provided, and thus would trigger the bug. This should minimize the impact on
users that were not encountering the bug.

DOC: Correct MV Normal sig

DOC: Minor rounding correction in Generator.binomial

Fix for #16508. Cython wants every pointer declaration to be on a
separate line.

Changed 38.88 from  38 to 39

Add new kw arg to sig

Broadcastable size with inputs does not produce an error when size produces
a smaller output array than the broadcast input shape. Patch checks that
the output shape matches the outer shape of the broadcast fo all inputs and
the size when given.

This requires some minor tweaks in `np.random` because there the two have different meanings, with `()` meaning 0d array and `None` meaning scalar.

Most compilers should optimize it, but it doesn't hurt to inline and has a better name
now.

DEP: Deprecate `numpy.dual`.