feat(新增水印处理单元测试): 在test_watermark_processor.py中新增多个测试用例，验证WatermarkProcessor和merge_watermark_config的功能，确保水印处理逻辑的准确性和可靠性。

ocr_utils/tests/test_watermark_processor.py

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+"""WatermarkProcessor 与 preset 单测。"""
+import numpy as np
+import pytest
+
+from ocr_utils.watermark import WatermarkProcessor, merge_watermark_config, get_preset
+
+
+def test_merge_cell_preset_has_mask():
+    cfg = merge_watermark_config("cell", {"method": "masked_adaptive"})
+    assert cfg["method"] == "masked_adaptive"
+    assert "mask" in cfg
+    assert cfg["mask"]["hough_min_line_length"] < get_preset("page", "masked_adaptive")["mask"][
+        "hough_min_line_length"
+    ]
+
+
+def test_processor_disabled_passthrough():
+    proc = WatermarkProcessor({"enabled": False}, scope="cell")
+    img = np.ones((40, 80, 3), dtype=np.uint8) * 255
+    out, stages = proc.process(img)
+    assert stages == []
+    assert out.shape == img.shape
+
+
+def test_processor_cell_force_wm():
+    proc = WatermarkProcessor(
+        {"enabled": True, "method": "masked_adaptive"}, scope="cell"
+    )
+    img = np.ones((50, 100, 3), dtype=np.uint8) * 240
+    cv2 = pytest.importorskip("cv2")
+    for x in range(0, 100, 8):
+        cv2.line(img, (x, 0), (x + 30, 50), (180, 180, 180), 1)
+    out, stages = proc.process(img, force=True)
+    assert "wm" in stages
+    assert out.shape == img.shape