add units to summary hyst table - #915

Closes #889

The summary table displayed by rmag.process_hyst_loop / rmag.process_hyst_loops reported parameter values without units. Column headers now spell them out:

Ms (Am²/kg) Mr (Am²/kg) Bc (T) Brh (T) sigma Q Qf chi_HF (m³/kg) FNL60 FNL70 FNL80

Parameters that are ratios, logarithms of ratios, or F statistics (Q, Qf, sigma, the FNL family) are dimensionless and stay bare; the closure-test ratios shown at the open-loop decision-tree exit (SNR, HAR) are labeled dB. The TableColumn field names are unchanged, so nothing downstream of the display shifts.

Changes

• New unit lookup tables and two helpers, _hyst_param_unit and _hyst_param_label, at the top of the hysteresis section of rockmag.py. _show_hyst_summary_table uses them for its headers, so all three decision-tree outcomes (full processing, linear loop, open loop) are labeled consistently.
• The susceptibility unit is derived rather than hardcoded. chi_HF is returned as μ₀·dM/dB, so its unit is the magnetization unit times m/A: Am²/kg → m³/kg, A/m → SI (dimensionless), Am² → m³. An unrecognized magnetization unit leaves chi_HF unlabeled rather than guessing.
• Added a magn_unit keyword (at the end of the signature) to process_hyst_loop, plot_hyst_loop, and process_hyst_loops. It only labels output — no values are converted. In process_hyst_loops it defaults to None and is inferred from the MagIC column name (magn_mass → Am²/kg, magn_volume → A/m, magn_moment → Am²), so the usual call needs no new argument while volume-normalized data is no longer mislabeled as mass-normalized.
• The hysteresis plot y-axis label, previously hardcoded to Am²/kg in both the Bokeh and matplotlib paths, now follows the same unit.
• Docstring Returns sections state the unit of each reported quantity. process_hyst_loops additionally notes that the returned DataFrame's column names deliberately carry no units, since renaming them would break add_hyst_stats_to_specimens_table and the specimens-table writers.
• Incidental fix: the comment explaining _HYST_UNDEFINED_RESULTS had drifted above _show_hyst_summary_table; it is back on the constant it describes.

Tests

New TestSummaryTableUnits class in pmagpy/test/test_rockmag_hysteresis.py covers the unit of each reported parameter, the chi_HF/magnetization-unit relation including the unrecognized-unit fallback, the rendered DataTable headers (with the field names verified unchanged), and the magn_col → unit inference in batch processing.

All 62 tests in the hysteresis suite pass, as do the curie, unmixing, and FORC suites (303 tests).

🤖 Assisted by Claude Opus 5 in code development.