Complete MultiLeader host model coverage

Extends the adapter generator (Color, LineWeight, mixed unit/payload enums,
fixed float arrays, bitflags-2 newtypes, keep_types override) and maps
MultiLeader with a merge-style context patch, host validation and
reference checks. staged_python_multileader_lifecycle_over_real_ipc passes
the full gate including DWG and DXF reopen.

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

plugins/opencad-python/src/patch_helpers.rs.inc

@@ -0,0 +1,23 @@
+// Merge helpers for nested structs that scripts edit as a partial patch.
+
+/// Apply `patch` (a dict of context fields) onto `existing`, so a script can
+/// change one context field without resetting the rest. Unknown keys error.
+fn merge_multileader_context(
+    existing: &acadrust::entities::MultiLeaderAnnotContext,
+    patch: PyObjectRef,
+    vm: &VirtualMachine,
+) -> PyResult<acadrust::entities::MultiLeaderAnnotContext> {
+    let patch = patch.try_into_value::<rustpython_vm::builtins::PyDictRef>(vm)?;
+    let merged = multi_leader_annot_context_to_dict(vm, existing)?
+        .try_into_value::<rustpython_vm::builtins::PyDictRef>(vm)?;
+    for key in patch.keys_vec() {
+        let name = key.clone().try_into_value::<String>(vm)?;
+        if merged.get_item_opt(name.as_str(), vm)?.is_none() {
+            return Err(vm.new_value_error(format!(
+                "ocs: MultiLeader.context property {name:?} is outside the editable schema"
+            )));
+        }
+        merged.set_item(name.as_str(), patch.get_item(name.as_str(), vm)?, vm)?;
+    }
+    dict_to_multi_leader_annot_context(merged.into(), vm)
+}