fix: 修复多占位符识别，补充测试

tests/create_fixtures.py

@@ -5,6 +5,7 @@ ws = wb.active
 ws.title = "Sheet1"
 ws["B3"] = "{{编号}}"
 ws["C5"] = "{{姓名}}"
-ws["D7"] = "normal_value"  # not a placeholder, should NOT be detected
+ws["D7"] = "normal_value"  # 非占位符，不应被识别
+ws["E9"] = "{{客户名}}和{{编号}}"  # 同一单元格内有两个占位符
 wb.save("tests/fixtures/sample_template.xlsx")
 print("fixture created")

tests/python/test_parser.py

@@ -26,3 +26,12 @@ def test_placeholder_has_cell_info():
     biaohao = next(p for p in result["placeholders"] if p["name"] == "编号")
     assert biaohao["sheet"] == "Sheet1"
     assert biaohao["cell"] == "B3"
+
+def test_multiple_placeholders_in_one_cell():
+    result = parse_template(FIXTURE)
+    names = [p["name"] for p in result["placeholders"]]
+    assert "客户名" in names
+    assert "编号" in names  # 已在其他地方存在，但也在 E9 中
+    # 验证 E9 中的两个占位符都被检测到
+    e9_placeholders = [p for p in result["placeholders"] if p["cell"] == "E9"]
+    assert len(e9_placeholders) == 2