6x speed up within() method of multiellipsoid

[segasai]

Speeds up this by a factor of 6

import dynesty.bounding as db
import numpy as np

sig = np.identity(10)
cens = [(np.arange(10) == i).astype(int) for i in range(10)]
ells = db.MultiEllipsoid([db.Ellipsoid(xcen, sig) for xcen in cens])
x0 = np.zeros(10)
for i in range(1000000):
    ells.within(x0)

[coveralls]

Pull Request Test Coverage Report for Build 1219412557

• 8 of 9 (88.89%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.004%) to 81.779%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
py/dynesty/bounding.py	4	5	80.0%
<!--	Total:	8	9	88.89%	-->

Totals
Change from base Build 1207209309:	-0.004%
Covered Lines:	3393
Relevant Lines:	4149

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💛 - Coveralls