Auto-discover major and minor technology when opening FORM input files

[barnaliy]

technology.hpp already encodes major/minor technology via Combine(major, minor) and GetMajor()/GetMinor() helpers. However, form_interface currently requires the user to explicitly specify the minor technology (e.g. ROOT_TTREE vs ROOT_RNTUPLE) in the configuration.
When opening an input file, FORM should be able to detect the major and minor technology automatically. This requires adding a discovery API to form_interface or the underlying storage layer.

Related to PR #379.

[gemmeren]

Thanks @barnaliy
Agreed, on file opening/reading the minor technology should be discovered.
But I am not sure that "This requires adding a discovery API to form_interface or the underlying storage layer." is really necessary. File opening could work with "ROOT_MAJOR" and only containers need the minor technology. An extra API layer, in my view, should be avoided.

[barnaliy]

Thanks @gemmeren. That was my quick thought on how to address it, but you're likely right—we might not need an extra API layer at all if the file opening logic handles the major technology. I'm glad you left the note, now whoever picks this up will have that context right away.