Vegas

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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().

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- Adds new keywords save and saveall for Integrators. These allow
the integrator to save results in a file automatically at the end of
each iteration. See "Saving Results Automatically" in the tutorial
for more details and examples.

- Pickled integrators now include information about the adaptive
stratified sampling as well as the adaptive importance sampling
(integ.map). This makes for larger files but now captures the
complete state of the integrator. The AdaptiveMap integ.map can
be pickled by itself, in a smaller file, if that is all that is
neeeded.

- Adds new function ravg for manipulating vegas results.

- Added extend method to results returned by vegas Integrators
that allow results from different runs to be merged.

- Bug fixes for pickling of integrators and integration results.
Can nnow use either pickle.dump/load or gvar.dump/load.

- Fixed pickling of Integrator so it handles nstrat properly.