NIAC 2025: updates to the codebase

[lukaspie]

As soon as the NIAC release will be stable, we need to address this in pynxtools as well. This is a summary issue to keep track of the individual items.

• update definitions, depends on Fairmat definitions sync with NIAC 2025 nexus_definitions#325
• enable use of identifierNAME in NXobject #514
• NIAC resolution for uppercases #441
• Add support for NXDL choices #240
• NeXus version management #275
• support NeXus reserved prefixes and suffixes #515
• Implement nameType="partial" #516
• unit examples in the nxdl file, such as eV/mm #517
• Possibly, if accepted: open enumerations (Allow for open enumerations nexusformat/definitions#1521)

Potentially relevant, but maybe need more clarification with NIAC:

• Variants: Apparently, you can write the following:

   beam_center_x
           @variant=beam_center_x_refined
   beam_center_x_refined
           @variant=beam_center_x_initial_guess
  

  and that tells you that these fields are variants of each other. They are chained through the @variant attribute? Do we want to support this?