refactor: extract src/ifcutil/ from src/ifcviewer/ (Unit, Geolocation, Placement)

Unit / Geolocation / Placement are schema-agnostic IFC helpers ported
from ifcopenshell.util.{unit,geolocation,placement}. Nothing about
them is viewer-specific: pure IfcParse + Eigen, no Qt, no IfcGeom, no
renderer. Living under src/ifcviewer/ implies an unwanted dependency
direction every time a non-viewer caller (test_federation, the bonsai
SettingsView georef readout, a future standalone IFC tool) wants to
use them.

Move them to a new `src/ifcutil/` static lib (IfcUtil). The lib has
PUBLIC `target_include_directories(${CMAKE_CURRENT_SOURCE_DIR})` so
callers that link IfcUtil can keep `#include "Unit.h"` etc. without
relative-path adjustments — the include dir propagates transitively
via IfcViewer's PUBLIC link.

## Changes

* `git mv src/ifcviewer/{Geolocation,Placement,Unit}.{h,cpp}
   → src/ifcutil/` (history follows the rename).
* `src/ifcutil/CMakeLists.txt`: IfcUtil static lib, PUBLIC links
  IfcParse + Eigen3::Eigen, PUBLIC include dir.
* `cmake/CMakeLists.txt`: `add_subdirectory(../src/ifcutil ifcutil)`
  before ifcviewer/ so the link target exists when IfcViewer's
  CMakeLists runs.
* `src/ifcviewer/CMakeLists.txt`: IfcUtil added to IfcViewer's PUBLIC
  link_libraries.
* `src/ifcviewer/tests/CMakeLists.txt`: test_federation drops the
  explicit `${IFCVIEWER_SRC}/{Unit,Geolocation,Placement}.cpp`
  source list and links `IfcUtil` instead (matches how production
  code resolves the symbols).
* `src/bonsaiviewer/modules/models/SettingsView.cpp`: the two
  explicit `#include "../../../ifcviewer/{Geolocation,Unit}.h"`
  paths swap to `../../../ifcutil/…`. All other callers use bare
  `#include "Unit.h"` style and continue to work via the propagated
  include dir.

## Verification

* `ninja -C build-viewer` builds clean: IfcUtil + IfcViewer +
  IfcViewerMinimal + BonsaiViewer + all four pre-existing
  ifcviewer tests + the two from-wgpu tests.
* `test_federation` runs green: 226 assertions in 22 test cases
  pass with IfcUtil linked instead of the explicit-source compile.
* `git log --follow` traces e.g. `Geolocation.cpp` back through the
  rename to its prior location in src/ifcviewer/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ifcviewer/tests/CMakeLists.txt

@@ -66,15 +66,6 @@ find_package(Eigen3 REQUIRED)
 add_executable(test_federation
     test_federation.cpp
     ${IFCVIEWER_SRC}/Federation.cpp
-    # Federation pulls in Unit::convert for federationUnitToMeters and
-    # Geolocation helpers (helmertMetersFromParameters, getWcs, getMapUnit)
-    # for computeModelGeoref; compile both directly so the test doesn't
-    # have to link the whole IfcViewer library (which would drag in
-    # Qt6::OpenGL, OpenCASCADE, etc.).  Placement.cpp provides
-    # getAxis2Placement, called from Geolocation::getWcs.
-    ${IFCVIEWER_SRC}/Unit.cpp
-    ${IFCVIEWER_SRC}/Geolocation.cpp
-    ${IFCVIEWER_SRC}/Placement.cpp
 )
 set_target_properties(test_federation PROPERTIES AUTOMOC ON)
 target_include_directories(test_federation PRIVATE ${IFCVIEWER_SRC})
@@ -84,6 +75,11 @@ target_link_libraries(test_federation PRIVATE
     Qt${QT_VERSION}::Gui    # Federation::HomeView uses QVector3D from QtGui
     Qt${QT_VERSION}::Test   # QSignalSpy
     Eigen3::Eigen           # Federation.h: composed matrices use Eigen
-    IfcParse                # Unit.cpp uses express::Base / file APIs
+    # IfcUtil provides Unit::convert + Geolocation helpers
+    # (helmertMetersFromParameters, getWcs, getMapUnit) + Placement
+    # (getAxis2Placement, called from Geolocation::getWcs). Linking the
+    # static lib avoids re-compiling those .cpp files here and pulls
+    # the IfcUtil include dir + IfcParse transitively.
+    IfcUtil
 )
 catch_discover_tests(test_federation)