fastbootd: Fix transport ownership.

This change moves Transport ownership back out of FastBootDriver.
Callers of set_transport must ensure that the previous transport is
destroyed. In addition, deleting a transport now ensures that it is
closed.

Bug: 78793464
Test: fastboot, fuzzy_fastboot works
Change-Id: I8f9ed2f7d5b09fd0820b2677d087a027378f26db
diff --git a/fastboot/usb_osx.cpp b/fastboot/usb_osx.cpp
index 4d48f6e..ed02c4a 100644
--- a/fastboot/usb_osx.cpp
+++ b/fastboot/usb_osx.cpp
@@ -70,7 +70,7 @@
     // A timeout of 0 is blocking
     OsxUsbTransport(std::unique_ptr<usb_handle> handle, uint32_t ms_timeout = 0)
         : handle_(std::move(handle)), ms_timeout_(ms_timeout) {}
-    ~OsxUsbTransport() override = default;
+    ~OsxUsbTransport() override;
 
     ssize_t Read(void* data, size_t len) override;
     ssize_t Write(const void* data, size_t len) override;
@@ -471,6 +471,10 @@
     return new OsxUsbTransport(std::move(handle), timeout_ms);
 }
 
+OsxUsbTransport::~OsxUsbTransport() {
+    Close();
+}
+
 int OsxUsbTransport::Close() {
     /* TODO: Something better here? */
     return 0;