gplepage/vegas: vegas version 6.4.1

New function vegas.restratify(integ, f) creates a copy of integrator integ but with a new y-space stratification that is adapted to integrand f(x). This is especially useful for high-dimension integrals where integration is particularly challenging in a small number of directions.

New vegas.Integrator option correlate_integrals if True (default) instructs vegas to evaluate correlations between the different integrals when integrating multiple integrands at the same time. Correlations are set to zero if the option is False, which can be faster but loses potentially useful information.

Bugs are fixed for pickling objects of type vegas.RAvgDict (for Python 3.14), and for vegas.Integrator(integ) where integ is an integrator.