feat(video): capture scanlines and prepare sprites one row ahead

Add cycle40 preparation, deferred diagnostics, HBlank capture, VBlank presentation, and affine history tests.

tests/scanlines.rs

@@ -0,0 +1,38 @@
+use gba_rust::{
+    cpu::Cpu,
+    display::{CYCLES_PER_FRAME, CYCLES_PER_LINE, HBLANK_START, VBLANK_START},
+    dma::DMA_BASE,
+    input::{Button, Buttons},
+    io::*,
+    machine::{Machine, StepKind},
+    memory::{Memory, OAM_START as OAM, PALETTE_START as PAL, ROM_START, VRAM_START as VRAM},
+    raster_demo::{RasterDemo, RASTER_STATE, RASTER_TABLE},
+    video::{rgb555_to_rgb888 as rgb, Framebuffer, VideoError, HEIGHT, WIDTH},
+};
+
+#[path = "scanlines/capture.rs"]
+mod capture;
+#[path = "scanlines/machine.rs"]
+mod machine;
+#[path = "scanlines/rendering.rs"]
+mod rendering;
+
+fn memory() -> Memory {
+    let mut m = Memory::new(vec![]).unwrap();
+    m.set_scanline_rendering(true);
+    m
+}
+
+fn present(m: &Memory) -> Framebuffer {
+    let mut f = Framebuffer::default();
+    assert!(m.present_frame(&mut f).unwrap());
+    f
+}
+
+fn at(f: &Framebuffer, x: usize, y: usize) -> u32 {
+    f.pixels()[y * WIDTH + x]
+}
+
+fn word_rom(code: &[u32]) -> Vec<u8> {
+    code.iter().flat_map(|v| v.to_le_bytes()).collect()
+}