Derive map units from IFC scale

Use IfcMapConversion.Scale as the source of truth for converting map coordinates to metres, instead of deriving that scale from IfcProjectedCRS.MapUnit. Bump the sidecar version because cached georef matrices and unit scales may differ under the new interpretation.

Generated with the assistance of an AI coding tool.

src/ifcviewer/tests/test_sidecar_cache.cpp

@@ -155,7 +155,7 @@ bool sidecarDataEqual(const SidecarData& a, const SidecarData& b) {
 TEST_CASE("MeshInfo and InstanceCpu have stable layouts (sidecar wire format)", "[sidecar]") {
     REQUIRE(sizeof(MeshInfo) == 56);
     REQUIRE(sizeof(InstanceGpu) == 80);
-    REQUIRE(SIDECAR_VERSION == 12);
+    REQUIRE(SIDECAR_VERSION == 13);
     REQUIRE(SIDECAR_MAGIC == 0x49465657u);
 }