Fix all ty diagnostics on ifcviewer-wgpu (ci-lint ty-ios + ty-bonsai)

This branch carried v0.8.0's strict `[tool.ty.rules] all = "error"` config but
not the source fixes that were made upstream to satisfy it, so both ci-lint ty
gates were failing: `poe ty-ios` reported 256 diagnostics and `poe ty-bonsai`
258. Both are now clean.

Most fixes are ported from v0.8.0 and follow two idioms: initialise a name
before a conditional that may not bind it (plus an `assert` where the invariant
is real but not provable), and close an exhaustive `if`/`elif` chain with
`else: assert False, <discriminant>`.

The branch's own newer accessors are preserved throughout - `.file`,
`.declaration`, `file.types()`, `get_max_id()` are kept rather than reverted to
`wrapped_data.*`, and non-ty upstream changes (notably the in-progress geometry
cache removal) are deliberately not pulled in.

Notable fixes that are not straight ports:

* ifcopenshell_wrapper.pyi: `entity_instance.file` was declared as
  `def file(self) -> file`, where the property name shadows the `class file`
  below it, so the annotation resolved to `Unknown`. Every `element.file` in
  the codebase was therefore unchecked. Qualifying it to `ifcopenshell.file`
  restores `.schema` to its Literal union and surfaces no new diagnostics.

* model/wall.py: a duplicated merge fragment in the void-straddle path ran an
  always-true `if void_straddles:` that read `new_opening` from the mutually
  exclusive branch (stale value, or NameError on the first iteration), followed
  by an unreachable duplicate `elif`. Removing it makes the file match v0.8.0.

* light/operator.py: upstream's own fix unpacks three targets from two values
  and raises ValueError unconditionally; corrected to `None, None, None`.

* assign_system.py, validate.py, geom/main.py: walrus-in-genexp is valid at
  runtime (PEP 572 binds in the containing scope) but ty does not model it;
  rewritten as explicit loops, matching upstream.

Verified: poe ty-ios, poe ty-bonsai, ruff check src/ nix/, black --check .,
and compileall -W error at py3.10 (ifcopenshell-python) and py3.11 (bonsai).

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

src/ifcopenshell-python/ifcopenshell/api/alignment/_add_segment_to_curve.py

@@ -159,8 +159,10 @@ def _add_segment_to_curve(
     else:
         assert False
 
+    end_point = ...
     for mapped_segment in mapped_segments:
         if mapped_segment:
             end_point = _add_curve_segment_to_composite_curve(file, layout_segment, mapped_segment, curve)
 
+    assert end_point is not ...
     return end_point

src/ifcopenshell-python/ifcopenshell/api/alignment/_get_segment_start_point_label.py

@@ -308,5 +308,7 @@ def _get_segment_start_point_label(prev_segment: entity_instance, segment: entit
             label = _cant_callback(prev_segment, segment)
         else:
             label = _cant_label(prev_segment, segment)
+    else:
+        assert False, s.DesignParameters
 
     return label

src/ifcopenshell-python/ifcopenshell/api/alignment/create_as_polyline.py

@@ -46,6 +46,7 @@ def _create_layout(file: ifcopenshell.file, alignment: entity_instance, points:
     ifcopenshell.api.nest.assign_object(file, related_objects=alignment_layouts, relating_object=alignment)
 
     start_dist_along = 0.0
+    gradient = None
     for p1, p2 in zip(points, points[1:]):
         x1, y1, z1 = p1.Coordinates
         x2, y2, z2 = p2.Coordinates
@@ -100,6 +101,7 @@ def _create_layout(file: ifcopenshell.file, alignment: entity_instance, points:
     ifcopenshell.api.nest.assign_object(file, related_objects=[hsegment], relating_object=alignment_layouts[0])
 
     if include_vertical:
+        assert gradient is not None
         vsegment = file.createIfcAlignmentSegment(
             ifcopenshell.guid.new(),
             DesignParameters=file.createIfcAlignmentVerticalSegment(

src/ifcopenshell-python/ifcopenshell/api/alignment/create_from_csv.py

@@ -57,6 +57,7 @@ def create_from_csv(file: ifcopenshell.file, filepath: str) -> entity_instance:
     :param filepath: path the to CSV file
     :return: IfcAlignment
     """
+    alignment = None
     with open(filepath, newline="") as csvfile:
         reader = csv.reader(csvfile)
         row_count = 0
@@ -89,9 +90,11 @@ def create_from_csv(file: ifcopenshell.file, filepath: str) -> entity_instance:
                 )
             else:
                 # add all subsequent vertical alignments
+                assert alignment is not None
                 vertical_layout = ifcopenshell.api.alignment.add_vertical_layout(file, alignment)
                 ifcopenshell.api.alignment.layout_vertical_alignment_by_pi_method(
                     file, vertical_layout, coordinates, radii
                 )
 
+    assert alignment is not None
     return alignment