fix(build): restore the no-default-features build, and drop lzma-sys

Two things the truck removal broke without saying so, both found by auditing
what is left in the manifest rather than by anything failing.

The cfg gate on `acis_export` ended up on `acad_to_render` instead, when that
module was put back after being deleted by mistake. `acad_to_render` is what
every entity converts through, so gating it left the wasm build — which is
what `--no-default-features` stands in for — unable to resolve it from thirty
places. It built at the commit before the migration and builds again now.

And deleting TRUCK_CHORD_FRAC took the constant but left its doc comment and
its `#[cfg]` behind, so the attribute landed on the next constant down and
gated a boundary-sampling tolerance that has nothing to do with solids.

lzma-sys was the last dependency in the manifest with nothing using it: no
code references it and nothing else in the tree pulls it in. The `solid3d`
feature it hung off still gates four places, so the feature stays.

Everything else declared is used. `getrandom` and `iced_widget` look unused
by grep and are not — the first is declared to turn on the feature the wasm
target needs from a crate half the tree pulls in, and the second is a
`[patch]` entry rather than a dependency at all.

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

src/scene/convert/mod.rs

@@ -1,5 +1,5 @@
-#[cfg(feature = "solid3d")]
 pub mod acad_to_render;
+#[cfg(feature = "solid3d")]
 pub mod acis_export;
 pub mod acis_kernel;
 pub mod dgn_linestyle;