Add API.md with full API reference and Mermaid diagrams

[Copilot]

No structured API reference existed — only a README and Jupyter notebooks. This adds API.md as a dedicated, scannable API doc.

Contents

• 5 Mermaid diagrams

  • graph TD — package/module structure
  • flowchart LR — typical fit workflow (load → choose model → fit → visualise → export)
  • classDiagram — model taxonomy (NoYieldStress / YieldStress / Composite)
  • sequenceDiagram — make_par_widget branching logic (pre-fit vs defaults)
  • graph LR — runtime dependency map

• Model reference for all 15 models: LaTeX equation, parameter table (name, default, min, max, unit)

• Function reference for all public callables across rheofit.models, rheofit.rheodata, and rheofit.visualization, with signatures, parameter tables, and short usage snippets

Quick example (from the doc)

import rheofit.rheodata as rheodata
from rheofit.models import HB_model, fit_FC, show_parameter_table
from rheofit.visualization import plot_fit_res

exp = rheodata.cp2pc_pg
data = exp.datasets[0].data

result = fit_FC(HB_model, data)
show_parameter_table(result)
fig = plot_fit_res(result, show_par_values=True)

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