fix: fix unload in LLM and ModelHostObject to properly free memory

Author: barhanc

packages/react-native-executorch/common/rnexecutorch/host_objects/ModelHostObject.h

@@ -436,6 +436,7 @@ template <typename Model> class ModelHostObject : public JsiHostObject {
   JSI_HOST_FUNCTION(unload) {
     try {
       model->unload();
+      thisValue.asObject(runtime).setExternalMemoryPressure(runtime, 0);
     } catch (const RnExecutorchError &e) {
       jsi::Object errorData(runtime);
       errorData.setProperty(runtime, "code", e.getNumericCode());

packages/react-native-executorch/common/rnexecutorch/models/llm/LLM.cpp

@@ -255,6 +255,9 @@ int32_t LLM::getMaxContextLength() const {
   return runner_->get_max_context_length();
 }
 
-void LLM::unload() noexcept { runner_.reset(nullptr); }
+void LLM::unload() noexcept {
+  runner.reset(nullptr);
+  BaseModel::unload();
+}
 
 } // namespace rnexecutorch::models::llm

packages/react-native-executorch/src/controllers/LLMController.ts

@@ -121,6 +121,11 @@ export class LLMController {
         await ResourceFetcher.fs.readAsString(tokenizerConfigPath!)
       );
 
+
+      if (this.nativeModule) {
+        this.nativeModule.unload();
+      }
+
       this.nativeModule = await global.loadLLM(
         modelPath,
         tokenizerPath,