Isolate the PDF interpolation backend to support both LHAPDF and NeoPDF

.github/workflows/rust.yml

@@ -36,6 +36,7 @@ jobs:
           # `-C link-dead-code` is needed to prevent 'warning: XX functions have mismatched data' warnings
           RUSTFLAGS: '-Cinstrument-coverage -Clink-dead-code'
         run: |
+          export NEOPDF_DATA_PATH=/usr/local/share/LHAPDF
           # we need stderr, but we can't run test twice because it'll regenerate/modify the binaries which interferes with `llvm-cov`
           cargo test --features=applgrid,evolve,fastnlo,fktable --no-fail-fast 2> >(tee stderr 1>&2)
           # from https://stackoverflow.com/a/51141872/812178

CHANGELOG.md

@@ -9,7 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Added a `pineappl_grid_convolution_pids` to the C API
+- added a `pineappl_grid_convolution_pids` to the C API
+- added support for the [NeoPDF](https://qcdlab.github.io/neopdf/) library as
+  an alternative to LHAPDF in the CLI; use `--backend=neopdf` to switch to it
 
 ## [1.4.2] - 31/05/2026