mtmd : DeepSeek-OCR image processing fixes, img_tool::resize padding refactor (#23345)

* mtmd : deepseek-ocr fixes, improvements and refactoring

- image processing changes to achieve full parity with Pillow (reference impl)
- SAM mask casting only when flash-attn is on
- SAM refactor (build_sam() extracted so deepseek-ocr-2 can reuse it)
- llama-chat changes to fix server/WebUI issue (new media_markers_first())
- adapted test-chat-template and added test cases for deepseek-ocr
- changed regression test for deepseek-ocr to use CER+chrF scores for ground-truth comparison; removed embedding-model
- ty.toml ignore unresolved-import for tools/mtmd/tests/**

* image-text reordering fix removed

* refactor bool add_padding + pad_rounding enum into a single pad_style enum

tools/mtmd/models/models.h

@@ -118,6 +118,7 @@ struct clip_graph_whisper_enc : clip_graph {
 struct clip_graph_deepseekocr : clip_graph {
     clip_graph_deepseekocr(clip_ctx * ctx, const clip_image_f32 & img) : clip_graph(ctx, img) {}
     ggml_cgraph * build() override;
+    ggml_tensor * build_sam(ggml_tensor * inp); // build the SAM model
 };
 
 struct clip_graph_conformer : clip_graph {