Add 60fps cutscene clamp for in-engine cinematics

Suspend the FPS unlock while a demo-manager Exec (DD sub_82184460 / EM sub_821856F8) ticks, so the frame-locked IngameCinematics Sequencer plays at native ~30fps instead of double speed. Adds ac6_cutscene_clamp CVar (default on).

out/build/win-amd64-relwithdebinfo/ac6recomp.toml

@@ -1,17 +1,15 @@
 # Auto-generated cvar configuration
-ac6_render_capture = false
-ac6_unlock_fps = false
-ac6_native_graphics_require_capture = false
-vsync = true
-guest_vblank_sync_to_refresh = true
-host_present_from_non_ui_thread = false
-d3d12_allow_variable_refresh_rate_and_tearing = false
 log_level = "debug"
 log_file = "ac6recomp.log"
+direct_host_resolve = false
+vfetch_index_rounding_bias = true
+guest_vblank_sync_to_refresh = true
+window_width = 1920
+window_height = 1080
 video_mode_width = 1920
 video_mode_height = 1080
 resolution = "1080p"
-direct_host_resolve = false
-window_width = 1920
-window_height = 1080
-vfetch_index_rounding_bias = true
+d3d12_allow_variable_refresh_rate_and_tearing = false
+host_present_from_non_ui_thread = false
+ac6_performance_mode = false
+ac6_unlock_fps = true