Consolidate workflow specifications, parameter models, and metadata mechanisms

Motivation

Avoid duplication, unify descriptions, etc. for UI generation and user info.

Relevant bits to be consolidated

• https://github.com/scipp/ess/blob/main/packages/essnmx/src/ess/nmx/configurations.py
• https://github.com/scipp/esslivedata/blob/main/src/ess/livedata/parameter_models.py
• Trimmed-down version of https://github.com/scipp/esslivedata/blob/aaf21dcf92a4df4e2b8b1e7278da96e02cd647b0/src/ess/livedata/config/workflow_spec.py#L246-L252
  Probably not for v1:
• Instrument-specific metadata (https://github.com/scipp/esslivedata/blob/aaf21dcf92a4df4e2b8b1e7278da96e02cd647b0/src/ess/livedata/config/instruments/loki/specs.py#L182-L227 )
• Models for inputs and outputs (example: https://github.com/scipp/esslivedata/blob/aaf21dcf92a4df4e2b8b1e7278da96e02cd647b0/src/ess/livedata/config/instruments/loki/specs.py#L120-L170)
  Maybe start by writing an ADR about a minimal solution so we can have a consensus about scope and shape?

Mandatory reading

I have previously done most of this analysis in scipp/esslivedata#889. Make sure to read it and in particular https://github.com/scipp/esslivedata/issues/889#issuecomment-4311180193 -- the attempt to consolidate everything ended up getting out of hand and blocked the entire work.

Read scipp/esslivedata#889 and especially the referenced comment before comparing configurations.py, parameter_models.py, and the trimmed workflow_spec.py section. Start by drafting an ADR for a minimal v1 consolidation, explicitly excluding instrument-specific metadata and input/output models. Done means the scope and shape have consensus before implementation begins.