refactor: use the built-in max/min to simplify the code (#17059)

### Summary

In Go 1.21, the standard library includes built-in
[max/min](https://pkg.go.dev/builtin@go1.21.0#max) function, which can
greatly simplify the code.

Signed-off-by: futurehua <futurehua@outlook.com>

internal/deepdoc/parser/pdf/table/table_layout.go

@@ -47,10 +47,7 @@ func layoutCleanup(cells []pdf.TSRCell, boxes []pdf.TextBox, far int, thr float6
 	i := 0
 	for i+1 < len(out) {
 		j := i + 1
-		limit := i + far
-		if limit > len(out) {
-			limit = len(out)
-		}
+		limit := min(i+far, len(out))
 		for j < limit && (out[i].Label != "" && out[i].Label != out[j].Label || notOverlapped(out[i], out[j])) {
 			j++
 		}

internal/deepdoc/parser/pdf/table/table_post.go

@@ -19,10 +19,7 @@ func FilterBoxesByRemoveSet(boxes []pdf.TextBox, removeSet map[int]bool) []pdf.T
 	}
 	// Pre-allocate: estimate final size to avoid resizing
 	// Use max to prevent negative capacity when len(removeSet) > len(boxes)
-	estimatedCap := len(boxes) - len(removeSet)
-	if estimatedCap < 0 {
-		estimatedCap = 0
-	}
+	estimatedCap := max(len(boxes)-len(removeSet), 0)
 	out := make([]pdf.TextBox, 0, estimatedCap)
 	for i, b := range boxes {
 		if !removeSet[i] {