Pattern for modifying workflows using `map` and `reduce`?

Context

Using Sciline's (Cycleban's) map/reduce we modify workflows. See scipp/esssans#135 and https://github.com/scipp/esssans/pull/135#discussion_r1629386269 for an example. The use of helper functions is not great UX (example: workflow = sans.with_banks(workflow, banks=[...])).

We should gain some more experience and get "data" on how well this works, then consider the alternatives below (or find more alternatives)

Alternatives

• Make this arguments of the workflow creation, LokiWorkflow(sample_runs=..., ...).
• Turn LokiWorkflow into a builder (using builder pattern):

  workflow = LokiWorkflow()
  workflow.set_sample_runs([...])
  workflow.build()  # or build automatically in `workflow.compute()`, by making this a wrapper.
  

• Turn LokiWorkflow into a wrapper, with internal reference to the pipeline. Dedicated methods can set and update the internal workflow.

Start by reviewing the map/reduce workflow example in scipp/esssans#135 and its linked pull-request discussion. Compare the current helper-function approach with the LokiWorkflow constructor, builder, and wrapper alternatives, or identify further options. The issue is complete when experience and data support a documented direction for the workflow-modification API.