add initial benchmark tests for asset loading

only for gif bitmaps right now, since i want to (eventually) clean that
up somewhat

libretrogd/Cargo.toml

@@ -30,3 +30,7 @@ harness = false
 [[bench]]
 name = "blit"
 harness = false
+
+[[bench]]
+name = "loading"
+harness = false

libretrogd/benches/loading.rs

@@ -0,0 +1,27 @@
+use std::io::Cursor;
+
+use criterion::{black_box, Criterion, criterion_group, criterion_main};
+
+use libretrogd::graphics::*;
+
+pub static SMALL_GIF_FILE_BYTES: &[u8] = include_bytes!("../test-assets/test.gif");
+pub static LARGE_GIF_FILE_BYTES: &[u8] = include_bytes!("../test-assets/test_image.gif");
+
+pub fn criterion_benchmark(c: &mut Criterion) {
+    c.bench_function("loading_small_gif", |b| {
+        b.iter(|| {
+            let mut reader = Cursor::new(SMALL_GIF_FILE_BYTES);
+            Bitmap::load_gif_bytes(black_box(&mut reader)).unwrap();
+        })
+    });
+
+    c.bench_function("loading_large_gif", |b| {
+        b.iter(|| {
+            let mut reader = Cursor::new(LARGE_GIF_FILE_BYTES);
+            Bitmap::load_gif_bytes(black_box(&mut reader)).unwrap();
+        })
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);