pythonPackages.pydicom: 1.3.0 -> 1.4.1

for pydicom: adds python 3.8 support (previously broken)

for nibabel:

• this unbreaks the package due to erroring tests in 3.0.0
• remove obsolete (mostly Python2-related) deps
• add deps to support MINC, DICOM, and SPM formats
• only build on x64 due to a dtype bug on Arm64

Refresh of #77472.

Depending package nilearn still fails to build for unrelated reasons [edit: fix pushed]. Also seems to be some issue with Nipype tests taking a long time/hanging with Python 3.8, but this was never building before. Will investigate these separately.

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• [NA] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.