Merge branch 'prvi-gmm-sigma-update' into 'main'

...a/gov/usgs/earthquake/nshmp/gmm/UsgsPrviBackbone2025.java

src/main/resources/gmm/coeffs/prvi-phiS2S-active-crust.csv

src/main/resources/gmm/coeffs/prvi-phiSS-active-crust.csv

src/main/resources/gmm/coeffs/prvi-sigma-subduction.csv

src/main/resources/gmm/coeffs/prvi-tau-active-crust.csv

src/test/resources/gmm/prvi-active-crust-results.csv

src/test/resources/gmm/prvi-interface-results.csv

src/test/resources/gmm/prvi-intraslab-results.csv