Viewport block caches no longer scan every object per entity

A drawing with 650k entities and 21k objects stalled for 7 minutes the
first time a layout viewport was drawn (#1746): building that viewport's
block cache asked for each entity's layer viewport overrides, and the
codec found each layer's extension dictionary by scanning every object
whenever the layer had none. Codec 2646725 reads the registered link.

The XCLIP check made the same scan for every nested INSERT without an
extension dictionary; it now reads the INSERT's own link, which the
readers and ensure_extension_dictionary always set.

Cargo: codec 2646725, kernel 4e6334a, graph 2fd1d42.

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

crates/ocs_plugin_api/Cargo.toml

@@ -15,7 +15,7 @@ serde_json = { version = "1", optional = true }
 # Pulled in only by the `host` feature, which adds the `opencadcodec`-typed
 # `HostApi` runtime surface. The default crate stays dependency-free so engine
 # crates and external tooling can depend on the manifest/ribbon contract cheaply.
-codec = { package = "acadrust", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "cf3a040", optional = true, features = ["serde"] }
+codec = { package = "acadrust", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "2646725", optional = true, features = ["serde"] }
 
 # Runtime IPC and serialization (host feature only).
 interprocess = { version = "2", optional = true }
@@ -39,7 +39,7 @@ serde_json = "1"
 serde = { version = "1", features = ["derive"] }
 cargo-lock = "11"
 # opencadcodec is scanned at build time to generate the embedded type registry.
-codec = { package = "acadrust", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "cf3a040", features = ["serde"] }
+codec = { package = "acadrust", git = "https://github.com/HakanSeven12/opencadcodec.git", rev = "2646725", features = ["serde"] }
 
 [dev-dependencies]
 serde_json = "1"