Integration With nirs4all

nirs4all-formats is a leaf I/O library. It does not depend on nirs4all.

The intended integration is:

1. load files with nirs4all-formats;

2. export arrays, axes and targets through Python or R bindings;

3. feed those outputs into nirs4all modelling pipelines;

4. preserve provenance so downstream models can report file origin and reader version.

SignalType and shared I/O types live here and can be re-exported by higher level projects.