add comparison

tests/benchmark_jpeg.nim

@@ -1,6 +1,19 @@
-import benchy, jpegsuite, pixie/fileformats/jpeg, strformat
+import benchy, jpegsuite, pixie/fileformats/jpeg, stb_image/read as stbi, strformat
 
 for file in jpegSuiteFiles:
   let data = readFile(file)
-  timeIt &"jpeg {(data.len div 1024)}k decode":
+  timeIt &"pixie jpeg {(data.len div 1024)}k decode":
     discard decodeJpeg(data)
+
+block:
+  for file in jpegSuiteFiles:
+    let data = readFile(file)
+    timeIt &"stb_image jpeg {(data.len div 1024)}k decode":
+      var width, height, channels: int
+      discard loadFromMemory(
+        cast[seq[byte]](data),
+        width,
+        height,
+        channels,
+        stbi.RGBA
+      )