The build process of ghostscript has missing dependencies, causing
failures in parallel builds (see hydra build
https://hydra.nixos.org/build/117095669/, reported as ghostscript bug
https://bugs.ghostscript.com/show_bug.cgi?id=702364 here)

libdvdread: 6.1.0 -> 6.1.1

pangomm: 2.42.0 -> 2.42.1

glibmm: 2.62.0 -> 2.64.2

libsecret: 0.20.2 -> 0.20.3

If a user provides `nativeBuildInputs = [ llvmPackages.bintools ]` or any other
package containing a `${prefix}/bin/diff`, the builder could use it instead
of the standard unix `diff`, causing a build failure.

This updates the call to specify an abspath to `diff` and avoid reliance on `PATH`.

Resolves #87081

Currently the tests take an eternity and are also sometimes flaky. By
following upstream in using xdist for parallel test execution we at
least get the feedback cycle down. On my machine that means instead of
running this for ~25min it runs in 1 minute and 10 seconds.

This is needed by newer versions of `tensorflow` and other ML tools, so we
should start working on an upgrade of the default versoin in the distribution.

…-schemas

When using netlib lapack/blas, the section name doesn’t match what
numpy expects. So we need to add extra sections for both so that the
right directory is found. The original “blas.implementation” section
may not actually be still required, but it is still a good idea so
that numpy know whether to apply any blas-implementation specific
quirks.

Fixes #86613

Some build systems look for this specifically.