fix(render): show Inventor drawing views, each in its own viewport (#1285)

Inventor DWG exports place every sheet block with AcIdBlockReference,
which the codec skipped, so these drawings opened blank. opencadcodec
7c20aa7 decodes it as an INSERT and keeps the viewport each model-space
view reference is bound to.

Those view blocks overlap in model space, so a content viewport now also
hides model-space references bound to a different viewport. The handles
join the viewport's frozen-layer set (entity and layer handles never
collide), which the wire and render-graph visibility checks and every
per-viewport cache key already use.

Pins opencadcodec 7c20aa7, opencadkernel d71a828, opencadgraph 1543a5a.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/opencad-python/Cargo.lock

@@ -1265,7 +1265,7 @@ dependencies = [
 [[package]]
 name = "opencadcodec"
 version = "0.5.5"
-source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=d6d534f#d6d534fcfec5823e47ef5630668d8e16d62c1641"
+source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=7c20aa7#7c20aa7fad405845c5bd5cdcc2a232cdc2a4687d"
 dependencies = [
  "ahash 0.8.12",
  "anyhow",