Fix headless build: add frame pacing stubs to null graphics backend

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

Author: tksuoran

src/erhe/graphics/erhe_graphics/null/null_device.cpp

@@ -141,6 +141,25 @@ auto Device_impl::get_native_handles() const -> Native_device_handles
     return Native_device_handles{};
 }
 
+auto Device_impl::wait_for_displayed_frame(const std::int64_t frame_id, const uint64_t timeout_ns) -> Present_wait_result
+{
+    static_cast<void>(frame_id);
+    static_cast<void>(timeout_ns);
+    return Present_wait_result::unsupported;
+}
+
+void Device_impl::set_present_target_time(const std::int64_t frame_id, const double target_time_seconds, const double hold_until_seconds)
+{
+    static_cast<void>(frame_id);
+    static_cast<void>(target_time_seconds);
+    static_cast<void>(hold_until_seconds);
+}
+
+auto Device_impl::get_frame_pacing_tier() const -> Frame_pacing_tier
+{
+    return Frame_pacing_tier::off;
+}
+
 void Device_impl::resize_swapchain_to_window()
 {
     // No-op for null backend

src/erhe/graphics/erhe_graphics/null/null_device.hpp

@@ -91,6 +91,9 @@ class Device_impl final
     [[nodiscard]] auto create_dummy_texture               (Command_buffer& init_command_buffer, erhe::dataformat::Format format) -> std::shared_ptr<Texture>;
     [[nodiscard]] auto get_buffer_alignment               (Buffer_target target) -> std::size_t;
     [[nodiscard]] auto get_frame_index                    () const -> uint64_t;
+    [[nodiscard]] auto wait_for_displayed_frame           (std::int64_t frame_id, uint64_t timeout_ns) -> Present_wait_result;
+                  void set_present_target_time            (std::int64_t frame_id, double target_time_seconds, double hold_until_seconds);
+    [[nodiscard]] auto get_frame_pacing_tier              () const -> Frame_pacing_tier;
     [[nodiscard]] auto allocate_ring_buffer_entry         (Buffer_target buffer_target, Ring_buffer_usage usage, std::size_t byte_count) -> Ring_buffer_range;
     [[nodiscard]] auto make_blit_command_encoder          (Command_buffer& command_buffer) -> Blit_command_encoder;
     [[nodiscard]] auto make_compute_command_encoder       (Command_buffer& command_buffer) -> Compute_command_encoder;