Add retro pairing in scalable seeker

Listen for manual pairing events and notify plugins.
Add retroactive pairing flow in the scalable seeker.
Actually upload the account key to the provider.
Missing bits:
- Notify the user and get their permission,
- Upload the new Account Key to user's account.

PiperOrigin-RevId: 544616348

fastpair/fast_pair_controller_test.cc

@@ -14,6 +14,7 @@
 
 #include "fastpair/fast_pair_controller.h"
 
+#include <memory>
 #include <string>
 
 #include "gmock/gmock.h"
@@ -45,6 +46,9 @@ class FastPairControllerTest : public testing::Test {
     NEARBY_LOGS(INFO) << "Provider address: " << address;
     remote_device_ = seeker_medium.GetRemoteDevice(provider_.GetMacAddress());
     ASSERT_TRUE(remote_device_.IsValid());
+    fast_pair_device_ =
+        std::make_unique<FastPairDevice>(Protocol::kFastPairRetroactivePairing);
+    fast_pair_device_->SetPublicAddress(remote_device_.GetMacAddress());
   }
 
   void TearDown() override {
@@ -60,14 +64,15 @@ class FastPairControllerTest : public testing::Test {
   Mediums mediums_;
   FakeProvider provider_;
   BluetoothDevice remote_device_;
+  std::unique_ptr<FastPairDevice> fast_pair_device_;
 };
 
 TEST_F(FastPairControllerTest, Constructor) {
-  FastPairController controller(&mediums_, remote_device_, &executor_);
+  FastPairController controller(&mediums_, &*fast_pair_device_, &executor_);
 }
 
 TEST_F(FastPairControllerTest, OpenMessageStream) {
-  FastPairController controller(&mediums_, remote_device_, &executor_);
+  FastPairController controller(&mediums_, &*fast_pair_device_, &executor_);
 
   EXPECT_OK(controller.OpenMessageStream());
 }