gh-1116: add resample_shapes()

[ntessore]

Description

Adds a new function glass.resample_shapes() that takes an array of ellipticity and randomises them. The function can optionally compensate for the intrinsic variance varg or vargamma of the (reduced) shear field (i.e., the variance of the ellipticities will be equal to the input array after applying a (reduced) shear).

Closes: #1116

Changelog entry

Added: A new function glass.resample_shapes() for resampling an existing catalogue of ellipticities.

Checks

• Is your code passing linting?
• Is your code passing tests?
• Have you added additional tests (if required)?
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[connoraird]

Looks good. I was also experiencing the failing examples, I'm not sure what's causing it.