Vegas

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- New default random number generator, to deal with
changes in numpy version >=1.17. Now tied explicitly to gvar's
random number generator (which is from numpy).

- Simpler and more robust implementation for vegas.__version__
(doesn't use importlib.metadata, which is buggy).

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Significantly improves handling of memory for internal work arrays. These
allocations are controlled by three parameters: min_neval_batch (new),
max_neval_hcube, and minimize_mem. Parameter min_neval_batch replaces
nhcube_batch, which is now ignored. The implementation for
minimize_mem=True is completely different and should be much faster
than before; this feature requires the h5py Python module.

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Improved build/installation code to handle systems with old versions of numpy
or new versions of Cython.

Support for wheels.

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Bug fixes to make code compatible with Cython v3.0 and numpy v1.25.

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* Integrator(itg) makes a more complete clone of Integrator itg than previously.

* Simpler and more modern installation setup with pyproject.toml, setup.cfg, ...

* Significant addition to the Tutorial section on Calculating Distributions.

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Fixes problem when integrating multiple integrands
simultaneously that are very different in magnitude.
Also adds new functionality to vegas.ravg().