Refactor: migrate pdf_parser.py to golang (#16323)

### What problem does this PR solve?

Http API based on onnx model.
pdf_parser.py to golang

### Type of change

- [x] Refactoring

internal/deepdoc/parser/pdf/mock_deepdoc_test.go

@@ -0,0 +1,75 @@
+package parser
+
+import (
+	"context"
+	"fmt"
+	"image"
+)
+
+// MockDocAnalyzer returns predefined data for unit tests.
+// Set an Err field to non-nil to exercise the corresponding error path.
+type MockDocAnalyzer struct {
+	DLARegions []DLARegion
+	TSRCells   []TSRCell
+	OCRBoxes   []OCRBox
+	OCRTexts   []OCRText
+	// OCRBatchTexts returns per-image texts for OCRRecognizeBatch.
+	// If nil, OCRTexts is returned for every image.
+	OCRBatchTexts [][]OCRText
+	// OCRBatchErr makes OCRRecognizeBatch return an error for image i.
+	OCRBatchErr func(i int) error
+	// Per-method error injection for testing failure paths.
+	DLAErr          error
+	TSRErr          error
+	OCRDetectErr    error
+	OCRRecognizeErr error
+
+	Healthy bool
+	Model   ModelType
+}
+
+func (m *MockDocAnalyzer) DLA(_ context.Context, _ image.Image) ([]DLARegion, error) {
+	if m.DLAErr != nil {
+		return nil, m.DLAErr
+	}
+	return m.DLARegions, nil
+}
+func (m *MockDocAnalyzer) TSR(_ context.Context, _ image.Image) ([]TSRCell, error) {
+	if m.TSRErr != nil {
+		return nil, m.TSRErr
+	}
+	return m.TSRCells, nil
+}
+func (m *MockDocAnalyzer) OCRDetect(_ context.Context, _ image.Image) ([]OCRBox, error) {
+	if m.OCRDetectErr != nil {
+		return nil, m.OCRDetectErr
+	}
+	return m.OCRBoxes, nil
+}
+func (m *MockDocAnalyzer) OCRRecognize(_ context.Context, _ image.Image) ([]OCRText, error) {
+	if m.OCRRecognizeErr != nil {
+		return nil, m.OCRRecognizeErr
+	}
+	return m.OCRTexts, nil
+}
+func (m *MockDocAnalyzer) OCRRecognizeBatch(_ context.Context, cropped []image.Image) ([][]OCRText, []error) {
+	results := make([][]OCRText, len(cropped))
+	errs := make([]error, len(cropped))
+	for i, img := range cropped {
+		if img == nil {
+			errs[i] = fmt.Errorf("image[%d] is nil", i)
+			continue
+		}
+		if m.OCRBatchErr != nil {
+			errs[i] = m.OCRBatchErr(i)
+		}
+		if m.OCRBatchTexts != nil && i < len(m.OCRBatchTexts) {
+			results[i] = m.OCRBatchTexts[i]
+		} else {
+			results[i] = m.OCRTexts
+		}
+	}
+	return results, errs
+}
+func (m *MockDocAnalyzer) Health() bool         { return m.Healthy }
+func (m *MockDocAnalyzer) ModelType() ModelType { return m.Model }