Show used against declared capacity where a master declares contact groups

Second half of #819: where a coil declares what contacts it provides, the
General tab now reports each type as used against declared rather than as
a bare count.

    NO : 3/4, NC : 1/2, inverseurs : 0/1, autres : 0/0

MasterElement::contactCapacity() sums contactCount over the element's
SlaveContactGroup list, per type, reusing the same ContactUsage tally the
used count is built on. The mapping from ElementData::SlaveState onto the
tally's own type is factored into one helper so the used count and the
declared capacity cannot classify a contact differently.

Falls back to the plain count from the previous commit when an element
declares no groups, which is every element in the standard collection
today -- nothing in the corpus declares slaveContactGroups, so this
changes no existing display.

A type used beyond what is declared reads as e.g. "1/0". That is
deliberate: it says this contact does not fit the part.

Display only. Whether a declared capacity should also feed
MasterElement::isFull() is the open question in #819 and is not touched
here.

Verified end to end against a purpose-built fixture, since no existing
element exercises this path: a coil declaring two NO groups of two, one
NC group of two and one changeover group of one parses and reports
NO=4 NC=2 SW=1 other=0 total=7, matching the declaration exactly.
tst_contactusage gains a case covering capacity summed across groups
(10 cases, all passing).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

sources/qetgraphicsitem/masterelement.cpp

@@ -235,6 +235,28 @@ void MasterElement::aboutDeleteXref()
  * so they cannot disagree with each other.
  * @return the per type usage
  */
+namespace {
+
+	/**
+		Map the element data's contact type onto the tally's own, so that
+		the used count and the declared capacity cannot classify the same
+		contact type differently.
+	*/
+	ContactUsage::Type contactType(ElementData::SlaveState state)
+	{
+		switch (state)
+		{
+			case ElementData::NO:    return ContactUsage::NO;
+			case ElementData::NC:    return ContactUsage::NC;
+			case ElementData::SW:    return ContactUsage::SW;
+			case ElementData::Other: break;
+		}
+
+		return ContactUsage::Other;
+	}
+
+}
+
 ContactUsage MasterElement::contactUsage() const
 {
 	ContactUsage usage;
@@ -246,22 +268,32 @@ ContactUsage MasterElement::contactUsage() const
 		}
 
 		const ElementData &data = elmt->elementData();
-
-		ContactUsage::Type type = ContactUsage::Other;
-		switch (data.m_slave_state)
-		{
-			case ElementData::NO:    type = ContactUsage::NO;    break;
-			case ElementData::NC:    type = ContactUsage::NC;    break;
-			case ElementData::SW:    type = ContactUsage::SW;    break;
-			case ElementData::Other: type = ContactUsage::Other; break;
-		}
-
-		usage.addSlave(type, data.m_contact_count);
+		usage.addSlave(contactType(data.m_slave_state), data.m_contact_count);
 	}
 
 	return usage;
 }
 
+/**
+ * @brief MasterElement::contactCapacity
+ * The contacts this master declares it provides, by type, summed over its
+ * contact groups. A group stands for contactCount contacts of its type.
+ * Returns an empty tally when the element declares no groups, which is the
+ * case for every element in the standard collection today -- callers use
+ * that to decide whether a capacity is worth showing at all.
+ * @return the per type capacity
+ */
+ContactUsage MasterElement::contactCapacity() const
+{
+	ContactUsage capacity;
+
+	for (const auto &group : m_data.m_slave_contact_groups) {
+		capacity.addSlave(contactType(group.type), group.contactCount);
+	}
+
+	return capacity;
+}
+
 /**
  * @brief MasterElement::isFull
  * @return true if the master has reached its maximum number of slaves

sources/qetgraphicsitem/masterelement.h

@@ -49,6 +49,7 @@ class MasterElement : public Element
 		QRectF XrefBoundingRect() const;
 
 		ContactUsage contactUsage() const;
+		ContactUsage contactCapacity() const;
 		bool isFull() const; // Check Slave-Limit
 		
 	protected:

sources/ui/elementpropertieswidget.cpp

@@ -393,16 +393,32 @@ QWidget *ElementPropertiesWidget::generalWidget()
 			//Counted in contacts rather than in linked elements, so that a
 			//slave standing for several contacts is reported as the number
 			//of contacts it actually uses.
-		const ContactUsage usage =
-				static_cast<MasterElement *>(m_element.data())->contactUsage();
+		const MasterElement *master =
+				static_cast<const MasterElement *>(m_element.data());
+		const ContactUsage usage = master->contactUsage();
 
 		description_string += QString(tr("Nombre de contacts esclaves utilisés : %1\n")).arg(usage.total());
 
 			//The breakdown is what tells you which auxiliary block would
 			//satisfy this coil, so it is only worth printing once there is
 			//something to break down.
-		if (usage.total() > 0)
+		const ContactUsage capacity = master->contactCapacity();
+
+		if (capacity.total() > 0)
 		{
+				//The element declares contact groups, so it can say not
+				//only what has been used but what it has to offer. A type
+				//used beyond what is declared shows as e.g. "1/0", which
+				//is the point: it says this contact does not fit the part.
+			description_string += QString(tr("    NO : %1/%2, NC : %3/%4, inverseurs : %5/%6, autres : %7/%8\n"))
+					.arg(usage.no).arg(capacity.no)
+					.arg(usage.nc).arg(capacity.nc)
+					.arg(usage.sw).arg(capacity.sw)
+					.arg(usage.other).arg(capacity.other);
+		}
+		else if (usage.total() > 0)
+		{
+				//No declared groups, so a plain count of what is in use.
 			description_string += QString(tr("    NO : %1, NC : %2, inverseurs : %3, autres : %4\n"))
 					.arg(usage.no)
 					.arg(usage.nc)