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/tools/metadata.go

@@ -0,0 +1,90 @@
+package tools
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"unicode/utf8"
+)
+
+// ReadPythonTextMeta reads Python pipeline stage data from #@meta lines.
+func ReadPythonTextMeta(pyTextDir string) ([]PyResult, error) {
+	entries, err := os.ReadDir(pyTextDir)
+	if err != nil {
+		return nil, err
+	}
+	var results []PyResult
+	for _, e := range entries {
+		if !strings.HasSuffix(e.Name(), ".txt") {
+			continue
+		}
+		data, err := os.ReadFile(filepath.Join(pyTextDir, e.Name()))
+		if err != nil {
+			continue
+		}
+		py := PyResult{File: strings.TrimSuffix(e.Name(), ".txt"), TextLen: utf8.RuneCount(data)}
+		if idx := strings.LastIndex(string(data), "\n#@meta"); idx >= 0 {
+			var meta struct {
+				Chars          int `json:"chars"`
+				BoxesInitial   int `json:"boxes_initial"`
+				BoxesTextMerge int `json:"boxes_text_merge"`
+				BoxesVertMerge int `json:"boxes_vertical_merge"`
+				Sections       int `json:"sections"`
+			}
+			if json.Unmarshal(data[idx+7:], &meta) == nil {
+				py.Chars = meta.Chars
+				py.BoxesInitial = meta.BoxesInitial
+				py.BoxesTextMerge = meta.BoxesTextMerge
+				py.BoxesVertMerge = meta.BoxesVertMerge
+				py.Sections = meta.Sections
+				py.Pages = 0
+				py.TextLen = utf8.RuneCount(data[:idx])
+			}
+		}
+		results = append(results, py)
+	}
+	return results, nil
+}
+
+// ReadGoTextMeta reads Go pipeline stage data from #@meta lines.
+func ReadGoTextMeta(goTextDir string) ([]BatchResult, error) {
+	entries, err := os.ReadDir(goTextDir)
+	if err != nil {
+		return nil, err
+	}
+	var results []BatchResult
+	for _, e := range entries {
+		if !strings.HasSuffix(e.Name(), ".txt") {
+			continue
+		}
+		data, err := os.ReadFile(filepath.Join(goTextDir, e.Name()))
+		if err != nil {
+			continue
+		}
+		r := BatchResult{
+			File:    strings.TrimSuffix(e.Name(), ".txt"),
+			Pages:   1,
+			TextLen: utf8.RuneCount(data),
+		}
+		if idx := strings.LastIndex(string(data), "\n#@meta"); idx >= 0 {
+			r.TextLen = utf8.RuneCount(data[:idx]) // text only, exclude #@meta
+			var meta struct {
+				Chars    int `json:"chars"`
+				BoxesIn  int `json:"boxes_initial"`
+				BoxesTM  int `json:"boxes_text_merge"`
+				BoxesVM  int `json:"boxes_vertical_merge"`
+				Sections int `json:"sections"`
+			}
+			if json.Unmarshal(data[idx+7:], &meta) == nil {
+				r.Chars = meta.Chars
+				r.BoxesInitial = meta.BoxesIn
+				r.BoxesTextMerg = meta.BoxesTM
+				r.BoxesVertMerg = meta.BoxesVM
+				r.Sections = meta.Sections
+			}
+		}
+		results = append(results, r)
+	}
+	return results, nil
+}