Build folios only when needed, by default (stage D6)

Every project now opens without building its folios; a folio is built
when it is shown or something needs its items (QETProject::lazyFolios()).
QET_LAZY_FOLIOS is gone; QET_EAGER_FOLIOS=1 builds every folio on
opening, as before, for comparisons and troubleshooting. Comments that
named the old variable now say "lazy folios"; the tests switch modes
with the new one.

The first save of a .qet as .qetz still builds every folio: a .qet does
not say which program wrote it, so its folios are written again rather
than copied. A .qetz opens and saves without building.

ctest 96/96 by default and with QET_EAGER_FOLIOS=1; 342 corpus projects
save the same in all four arms and export the same. In the GUI
(qet-gui-dialog): a 136-folio .qetz opens with no folio built, shows
folios 1 to 4, saves building none, the save = the original but the time
spent in it; a .qet opens lazily, saves as a .qetz beside it after the
notice, the .qet unchanged.

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

sources/scripting/qetscriptapi.cpp

@@ -465,7 +465,7 @@ void QetScriptApi::setLive(QStringList *log)
 /**
 	@brief QetScriptApi::unbuiltInformation
 	@return the information of the symbol @p elementUuid on the folio
-	@p folioIndex when that folio is not built (QET_LAZY_FOLIOS) and the
+	@p folioIndex when that folio is not built (lazy folios) and the
 	symbol's information can be read and changed through the project
 	database alone (projectDataBase::canEditUnbuilt()); nothing otherwise,
 	the folio to be built
@@ -486,7 +486,7 @@ std::optional<DiagramContext> QetScriptApi::unbuiltInformation(int folioIndex, c
 
 /**
 	@brief QetScriptApi::built
-	@return @p folio, built if it was not yet (QET_LAZY_FOLIOS), as showing
+	@return @p folio, built if it was not yet (lazy folios), as showing
 	it builds it: what a call reading or changing its items needs. A
 	folio's own data (title block, border, wire defaults) needs no build.
 */