fix: hide block definition entities from viewport

Block-definition geometry (entities stored inside named blocks) was
leaking into the viewport when DXF files omit the owner-handle group
code (330) on block-content entities.

The fix tightens `belongs_to_visible_block`: when `owner_handle` is
null, the current layout block-record's `entity_handles` list is used
as the authoritative allow-list before falling back to the older
"not-in-any-other-block" heuristic.  This ensures block definitions
are never rendered directly, only when referenced via an INSERT.

Bumps version to 0.1.4.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Cargo.lock

@@ -4,7 +4,7 @@ version = 4
 
 [[package]]
 name = "H7CAD"
-version = "0.1.3"
+version = "0.1.4"
 dependencies = [
  "acadrust",
  "bytemuck",