ui: a measurement's noise band and HF reject are settable and persisted

Two rows in the measure dialog, built the way the threshold and side rows are and appended
beside them: the band as a percentage of the window's own peak-to-peak (the unit the engine
takes), the corner in Hz with 0 off. They are seeded when editing, shown only where they do
something -- the band for the crossing types, since it moves the edge decision and nothing
else, the reject for all of them, since it sits before both walks -- and read into
`MeasureOptions` on apply.

They persist as two *named* keys, `noise` and `hf`, on the same `o <<` chain as the keys
beside them and read back through the same keyed reader, so a session written before this
change loads with 10.0 and 0.0: today's behaviour exactly, with no version check.

[configs] now proves the round trip rather than assuming it. The probe sets the first
measurement's band and corner to 7.5 and 250 before saving, so a key that never reached the
file reads back as the defaults:

    [configs] round trip read=1 comment='written by the configs probe' ... measures=4 math=0 noise=7.5 hf=250

The rest of that line is unchanged, and the run is free of Gtk-CRITICAL.

src/ui_measure.cpp

@@ -94,6 +94,10 @@ void measure_dialog_sync(MeasureDialog* d) {
   const bool side = measure_uses_side(type);
   gtk_widget_set_visible(d->threshold_row, threshold);
   gtk_widget_set_visible(d->side_row, side);
+  // The band moves the edge decision, so it is shown for exactly the crossing types. The HF reject sits
+  // before both walks, so it is shown for all of them.
+  gtk_widget_set_visible(d->noise_row, measure_uses_noise(type));
+  gtk_widget_set_visible(d->hf_row, TRUE);
   gtk_widget_set_visible(d->show, measure_can_show_on_plot(type));
 
   // The words follow the type: one row, several meanings.
@@ -166,6 +170,8 @@ void on_measure_dialog_apply(GtkButton*, gpointer user) {
   m.options.threshold_pct = gtk_spin_button_get_value(GTK_SPIN_BUTTON(d->threshold));
   m.options.above = gtk_switch_get_active(GTK_SWITCH(d->above));
   m.options.show_on_plot = gtk_check_button_get_active(GTK_CHECK_BUTTON(d->show));
+  m.options.noise_pct = gtk_spin_button_get_value(GTK_SPIN_BUTTON(d->noise));
+  m.options.hf_fc = gtk_spin_button_get_value(GTK_SPIN_BUTTON(d->hf));
   if (d->edit >= 0 && static_cast<std::size_t>(d->edit) < app.measures.size()) {
     app.measures[static_cast<std::size_t>(d->edit)] = std::move(m);
   } else {