Fix gcc14 build errors with CUDA enabled

[michalkielan]

I observed a bunch of errors when compiling vmaf with CUDA enabled. Looks like those errors were exposed when using gcc-14. Running meson with gcc-13 works fine with no issues. This PR fixes errors that prevent me from compiling: explicit casting, missing headers, unused parameter.

Repro:

$ meson libvmaf/build libvmaf -Denable_cuda=true -Denable_avx512=true
$ ninja -vC libvmaf/build

System:

$ cat /etc/redhat-release
Fedora release 41 (Forty One)

$ gcc --version
gcc (GCC) 14.2.1 20250110 (Red Hat 14.2.1-7)
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[nilfm99]

LGTM, thanks!