避免原始 PNG 的重复解析

使用解码后的颜色类型校验位深，将读取限制统一留在 image 解码器。

server-rs/crates/api-server/src/raw_image.rs

@@ -374,18 +374,20 @@ fn decode_image(value: RawImageData, field: &str) -> Result<(ReferenceImage, u32
     if reader.format() != Some(ImageFormat::Png) {
         return Err(bad_request(format!("{field} 文件必须是有效 PNG 文件")));
     }
-    let png_decoder = png::Decoder::new(Cursor::new(bytes.as_ref()));
-    let png_reader = png_decoder
-        .read_info()
-        .map_err(|_| bad_request(format!("{field} 文件必须是有效 PNG 文件")))?;
-    if png_reader.info().bit_depth != png::BitDepth::Eight {
+    let decoded = reader
+        .decode()
+        .map_err(|error| map_decode_image_error(field, error))?;
+    if matches!(
+        decoded.color(),
+        image::ColorType::Rgba16
+            | image::ColorType::Rgb16
+            | image::ColorType::L16
+            | image::ColorType::La16
+    ) {
         return Err(bad_request(format!(
             "{field} 必须为 8-bit PNG（每通道 8 位）"
         )));
     }
-    let decoded = reader
-        .decode()
-        .map_err(|error| map_decode_image_error(field, error))?;
     let (width, height) = decoded.dimensions();
     Ok((
         ReferenceImage {