refactor: 优化图像输入源设计，重构为零污染的 TryFromImage 特征

- 移除原有的 ImageInput 枚举，避免运行时匹配与所有权限制
- 引入自定义 TryFromImage 特征，专用于将不同来源安全转换为 ImageSource
- 优化错误处理新增 InvalidBase64Header 错误信息
- 迁移 load_image_from_input 到 image_helper.rs 为后续剥离到业务层做准备

ddddocr-core/src/utils/image_processor.rs

@@ -1,6 +1,6 @@
-use image::{DynamicImage, GrayImage, ImageBuffer, Luma, imageops::FilterType};
+use image::{imageops::FilterType, DynamicImage, GrayImage, ImageBuffer, Luma};
 
-use ndarray::{Array2, Array3, ArrayView2, ArrayView3, azip};
+use ndarray::{azip, Array2, Array3, ArrayView2, ArrayView3};
 use std::cmp::{max, min};
 
 // 模拟openCV
@@ -174,8 +174,6 @@ pub fn rgb_to_opencv_hsv(r: u8, g: u8, b: u8) -> (u8, u8, u8) {
     (h_opencv, s_opencv, v_opencv)
 }
 
-
-
 /// 对应 Python 的 convert_to_grayscale
 /// 将图像转换为灰度图 (L模式)
 pub fn convert_to_grayscale(image: &DynamicImage) -> GrayImage {