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/table_builder.go

@@ -0,0 +1,22 @@
+package parser
+
+import (
+	"context"
+	"image"
+)
+
+// TableBuilder encapsulates TSR model-specific cell detection and grouping.
+// Each TSR model implements its own Builder, producing a unified row-column
+// grid consumed by the shared downstream pipeline.
+type TableBuilder interface {
+	// Name returns the model identifier for logging and diagnostics.
+	Name() string
+
+	// DetectCells detects all cells from a cropped table image.
+	// The Label field on returned TSRCells is consumed only by the Builder
+	// itself during GroupCells; shared code does not depend on Label semantics.
+	DetectCells(ctx context.Context, cropped image.Image) ([]TSRCell, error)
+
+	// GroupCells groups cells into a row-column grid (pure computation, no I/O).
+	GroupCells(cells []TSRCell) [][]TSRCell
+}