Add, move or remove a folio without building the others (stage D5)

Adding, moving or removing a folio rewrote every folio's position in
the project database through diagrams(), which builds every folio: 3 s
on a 50-folio project opened lazily. A folio not built has its position
and title block already, so folios() is enough. The list of tables a
table can continue builds only the folios holding a table (from the
index of a .qetz), and the wiring list's count of wires left out looks
at built folios only: reading a wire drops it unless both its ends are
found.

tst_lazyfolios: a folio added, moved and removed builds no other, with
the folios' rows as when every folio is built (fails with diagrams():
47 built); the tables listed as when built, building the 12 folios that
hold one (fails when every folio is built). ctest 96/96 eager and lazy;
342 corpus projects save the same in all four arms.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/qetproject.cpp

@@ -2978,6 +2978,27 @@ bool QETProject::usesElement(const ElementsLocation &location) const
 	return(unbuiltFolioElements().contains(location));
 }
 
+/**
+	@brief QETProject::buildFoliosHoldingTables
+	Build the folios not built yet (QET_LAZY_FOLIOS) that hold a drawn
+	table, found from the index the project was opened from when it has
+	one: what a list of the project's tables needs, and no more
+*/
+void QETProject::buildFoliosHoldingTables()
+{
+	QList<Diagram *> to_build;
+	for (Diagram *d : std::as_const(m_diagrams_list))
+		if (!d->isLoaded() && unbuiltFolioHasTables(d))
+			to_build << d;
+	if (to_build.isEmpty()) {
+		return;
+	}
+	if (qEnvironmentVariableIntValue("QET_LAZY_FOLIOS_TRACE") == 1) {
+		qWarning().noquote() << "lazy folios:" << to_build.size() << "folios built for their tables";
+	}
+	buildFolios(to_build);
+}
+
 /**
 	@brief QETProject::unbuiltFolioHasTables
 	@return true if @p folio, not built yet (QET_LAZY_FOLIOS), has a drawn