feat(plugin): name-addressed XRecord CRUD on the HostApi (API v8)

Add create/read/update/delete/list for XRecord objects under
named-object-dictionary paths to the plugin HostApi, with five additive
PluginRequest/PluginResponse variants, dispatch through the shared
handler, in-process HostSession methods and both out-of-process proxies.

- dictionary paths walk from the NOD root; create seeds missing
  dictionaries (ensure_image_dictionary bootstrap) and refuses existing
  names; update refuses missing ones; refusals precede the undo step
- entry group codes validated (1..=369, never 5/105); payload content is
  the plugin's own
- each mutating call is one undo step: the pending history snapshot
  restores the objects map byte-exactly, auto-created dictionaries
  included (tested)
- typed entries survive DWG and DXF write/reload round-trips (tested);
  update drops verbatim raw bytes so saves emit the new content
- bump API_VERSION 7 -> 8 with the build.rs version_info in lockstep,
  mirroring the v7 addition; MIN_SUPPORTED stays 3

crates/ocs_plugin_api/src/manifest.rs

@@ -21,8 +21,11 @@
 /// adds the `BuiltinPlugin::on_load` lifecycle callback and
 /// `HostApi::document_path`. v6 appends generic host system-variable access
 /// (`HostApi::system_variable` / `set_system_variable`). v7 appends atomic,
-/// undoable replacement of a set of existing entities.
-pub const API_VERSION: u32 = 7;
+/// undoable replacement of a set of existing entities. v8 appends name-addressed
+/// XRecord object CRUD under named-object-dictionary paths
+/// (`HostApi::create_xrecord` / `read_xrecord` / `update_xrecord` /
+/// `delete_xrecord` / `list_xrecords`).
+pub const API_VERSION: u32 = 8;
 
 /// Oldest plugin API major the current host still loads. This keeps previously
 /// compiled cdylibs usable as long as their vtable layout is a prefix of the