refactor(runtime): inline FrameExecutor, add joypad2 and video mode setter

Remove FrameExecutor indirection by inlining its logic into
RuntimeHostLoop. Add set_video_mode() for NTSC/PAL switching,
set_joypad2_buttons() for player 2 input, and fix mapper scanline
IRQ test timing.

src/runtime/host/loop_runner.rs

@@ -1,23 +1,35 @@
-use crate::runtime::{NesRuntime, RuntimeError};
+use crate::runtime::{
+    AudioMixer, FRAME_HEIGHT, FRAME_RGBA_BYTES, FRAME_WIDTH, NesRuntime, RuntimeError,
+};
 
 use super::clock::{FrameClock, NoopClock, PacingClock};
 use super::config::HostConfig;
-use super::executor::{FrameExecution, FrameExecutor};
 use super::io::{AudioOutput, InputProvider, VideoOutput};
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[non_exhaustive]
+pub struct FrameExecution {
+    pub frame_number: u64,
+    pub audio_samples: usize,
+}
+
 pub struct RuntimeHostLoop<C = PacingClock> {
     runtime: NesRuntime,
-    executor: FrameExecutor,
+    mixer: AudioMixer,
+    frame_buffer: Vec<u8>,
+    audio_buffer: Vec<f32>,
     clock: C,
 }
 
 impl RuntimeHostLoop<PacingClock> {
     pub fn new(runtime: NesRuntime, sample_rate: u32) -> Self {
-        let executor = FrameExecutor::from_runtime(&runtime, sample_rate);
+        let mixer = runtime.default_audio_mixer(sample_rate);
         let clock = PacingClock::from_runtime(&runtime);
         Self {
             runtime,
-            executor,
+            mixer,
+            frame_buffer: vec![0; FRAME_RGBA_BYTES],
+            audio_buffer: Vec::new(),
             clock,
         }
     }
@@ -26,7 +38,7 @@ impl RuntimeHostLoop<PacingClock> {
         runtime: NesRuntime,
         config: HostConfig,
     ) -> RuntimeHostLoop<Box<dyn FrameClock>> {
-        let executor = FrameExecutor::from_runtime(&runtime, config.sample_rate);
+        let mixer = runtime.default_audio_mixer(config.sample_rate);
         let clock: Box<dyn FrameClock> = if config.pacing {
             Box::new(PacingClock::from_runtime(&runtime))
         } else {
@@ -34,7 +46,9 @@ impl RuntimeHostLoop<PacingClock> {
         };
         RuntimeHostLoop {
             runtime,
-            executor,
+            mixer,
+            frame_buffer: vec![0; FRAME_RGBA_BYTES],
+            audio_buffer: Vec::new(),
             clock,
         }
     }
@@ -45,10 +59,12 @@ where
     C: FrameClock,
 {
     pub fn with_clock(runtime: NesRuntime, sample_rate: u32, clock: C) -> Self {
-        let executor = FrameExecutor::from_runtime(&runtime, sample_rate);
+        let mixer = runtime.default_audio_mixer(sample_rate);
         Self {
             runtime,
-            executor,
+            mixer,
+            frame_buffer: vec![0; FRAME_RGBA_BYTES],
+            audio_buffer: Vec::new(),
             clock,
         }
     }
@@ -65,12 +81,12 @@ where
         self.runtime
     }
 
-    pub fn executor(&self) -> &FrameExecutor {
-        &self.executor
+    pub fn mixer(&self) -> &AudioMixer {
+        &self.mixer
     }
 
-    pub fn executor_mut(&mut self) -> &mut FrameExecutor {
-        &mut self.executor
+    pub fn mixer_mut(&mut self) -> &mut AudioMixer {
+        &mut self.mixer
     }
 
     pub fn clock(&self) -> &C {
@@ -108,8 +124,20 @@ where
         V: VideoOutput,
         A: AudioOutput,
     {
-        self.executor
-            .execute_frame(&mut self.runtime, input, video, audio)
+        self.runtime.set_buttons(input.poll_buttons());
+        self.audio_buffer.clear();
+
+        self.runtime
+            .run_until_frame_complete_with_audio(&mut self.mixer, &mut self.audio_buffer)?;
+        self.runtime.render_frame_rgba(&mut self.frame_buffer)?;
+
+        audio.push_samples(&self.audio_buffer);
+        video.present_rgba(&self.frame_buffer, FRAME_WIDTH, FRAME_HEIGHT);
+
+        Ok(FrameExecution {
+            frame_number: self.runtime.frame_number(),
+            audio_samples: self.audio_buffer.len(),
+        })
     }
 
     pub fn run_frames<I, V, A>(