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/bonsai/test/bim/test_feature.py

@@ -30,7 +30,7 @@ from collections.abc import Generator
 from inspect import signature
 from math import radians
 from pathlib import Path
-from typing import Any, Union
+from typing import Any, Union, cast
 
 import bpy
 import ifcopenshell
@@ -140,7 +140,7 @@ class PanelSpy:
             else:
                 props = kwargs.get("data")
                 name = kwargs.get("property")
-            props: bpy.types.bpy_struct
+            props = cast(bpy.types.bpy_struct, props)
             text = kwargs.get("text", props.bl_rna.properties[name].name)
             icon = kwargs.get("icon", None)
             prop_type = props.bl_rna.properties[name].type