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/pdfoxide/cropbox.go

@@ -0,0 +1,109 @@
+package pdfoxide
+
+import "strconv"
+
+// parseCropBoxFromRaw scans raw PDF bytes for /CropBox entries and
+// returns the array [x0, y0, x1, y1] for the given page index (0-based).
+// The second return value is false if no /CropBox was found.
+//
+// Algorithm: sequential scan of "/CropBox [...]" patterns — same approach
+// as parsePageRotationFromRaw.  Works for all common PDF generators.
+func parseCropBoxFromRaw(data []byte, pageIdx int) ([4]float64, bool) {
+	type cb [4]float64
+	var boxes []cb
+	rest := data
+	for {
+		idx := indexAfter(rest, "/CropBox")
+		if idx < 0 {
+			break
+		}
+		rest = rest[idx:]
+		// Skip whitespace, expect '['
+		for len(rest) > 0 && isSpace(rest[0]) {
+			rest = rest[1:]
+		}
+		if len(rest) == 0 || rest[0] != '[' {
+			continue
+		}
+		rest = rest[1:]
+		// Parse 4 float values inside [...]
+		var vals [4]float64
+		ok := true
+		for i := 0; i < 4; i++ {
+			for len(rest) > 0 && isSpace(rest[0]) {
+				rest = rest[1:]
+			}
+			v, n := parseFloat(rest)
+			if n == 0 {
+				ok = false
+				break
+			}
+			vals[i] = v
+			rest = rest[n:]
+		}
+		if !ok {
+			continue
+		}
+		boxes = append(boxes, cb(vals))
+	}
+	if pageIdx < len(boxes) {
+		return boxes[pageIdx], true
+	}
+	return [4]float64{}, false
+}
+
+// indexAfter finds the byte position right after the first occurrence of s in
+// data. Returns -1 if not found.
+func indexAfter(data []byte, s string) int {
+	for i := 0; i < len(data)-len(s); i++ {
+		match := true
+		for j := 0; j < len(s); j++ {
+			if data[i+j] != s[j] {
+				match = false
+				break
+			}
+		}
+		if match {
+			return i + len(s)
+		}
+	}
+	return -1
+}
+
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}
+
+// parseFloat parses a decimal number from the beginning of s.
+// Returns the value and the number of bytes consumed (0 on failure).
+func parseFloat(s []byte) (float64, int) {
+	i := 0
+	for i < len(s) && isSpace(s[i]) {
+		i++
+	}
+	j := i
+	// Scan: optional sign, digits, optional decimal point + digits
+	if j < len(s) && (s[j] == '+' || s[j] == '-') {
+		j++
+	}
+	hasDigit := false
+	for j < len(s) && s[j] >= '0' && s[j] <= '9' {
+		j++
+		hasDigit = true
+	}
+	if j < len(s) && s[j] == '.' {
+		j++
+		for j < len(s) && s[j] >= '0' && s[j] <= '9' {
+			j++
+			hasDigit = true
+		}
+	}
+	if !hasDigit || j == i {
+		return 0, 0
+	}
+	v, err := strconv.ParseFloat(string(s[i:j]), 64)
+	if err != nil {
+		return 0, 0
+	}
+	return v, j
+}