combine l_moment, l_ratio and l_stats

[jorenham]

Introduce a new function (e.g. l_moments or just moments) that accepts max_order: int, / and kwargs first_order: int = 1 and ratio: bool = True, always returns an xp.Array (np.ndarray by default) of shape (max_order - first_order + 1,) and real floating dtype (dtype: type[xp.floating] = xp.float64), where ratio=True is like l_stats and ratio=False like l_moment.

Deprecate l_moment, l_ratio and l_stats on lmo<1, and remove them in the v1.0 release.

The current l_{loc,variation,scale,skew,kurt[osis]} should be modified to autonomically calculate these statistics, preferably as an array-api compatible gufunc-like (potentially delegating to a numba gufunc).

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The same can be done with theoretical ones in lmo.theoretical, and similarly in lmo.diagnostic.