build: prefer FlexiBLAS when the wrapper is present

conda-forge ships libblas/liblapack as ABI packages with no
FlexiBLAS build. The engine links FlexiBLAS first and falls
back to those names.

Author: HaoZeke

environment.yml

@@ -16,6 +16,8 @@ dependencies:
   - eigen
   - libblas
   - liblapack
+  # Meson prefers FlexiBLAS when pkg-config finds it. These are the
+  # conda-forge ABI packages (that channel has no FlexiBLAS build).
   - nanobind
   - numpy
   - pip