STEP export: Support overriding header metadata

[ubruhin]

When exporting STEP files like that (an assembly in my case):

assembly = cq.Assembly(name='foo')
# assembly.add(...)
assembly.save('out.step', 'STEP')

The exported file contains some metadata in the header:

FILE_DESCRIPTION(('Open CASCADE Model'),'2;1');
FILE_NAME('Open CASCADE Shape Model','2023-09-01T11:49:38',('Author'),(
    'Open CASCADE'),'Open CASCADE STEP processor 7.7','Open CASCADE 7.7'
  ,'Unknown');

It would be nice to make this medatada configurable. The most important part for us is the timestamp to allow generating deterministic output from librepcb-parts-generator, but of course it would also make sense to override other metadata.

In C++ I do it like that (it works for me, but I'm not an OCC expert):

STEPCAFControl_Writer writer;
writer.SetColorMode(Standard_True);
writer.SetNameMode(Standard_True);

APIHeaderSection_MakeHeader hdr(writer.ChangeWriter().Model());
hdr.SetDescriptionValue(1, new TCollection_HAsciiString("PCB Assembly"));
hdr.SetName(new TCollection_HAsciiString("my project"));
hdr.SetAuthorValue(1, new TCollection_HAsciiString(""));
hdr.SetOrganizationValue(1, new TCollection_HAsciiString(""));
hdr.SetOriginatingSystem(new TCollection_HAsciiString("LibrePCB"));
hdr.SetTimeStamp(new TCollection_HAsciiString("2000-01-01T00:00:00"));

Links to OCCT documentation:

• APIHeaderSection_MakeHeader
• STEPCAFControl_Writer