feat(python): add PP-OCRv6 paddle backend support (#696)

* feat(python): add PP-OCRv6 paddle backend support

- init_predictor + device_config: add PPOCRV6 to PPOCRV5 branches (PIR format, enable_new_ir/new_executor)

- have_key + get_character_list: read character_dict from inference.yml instead of always returning False

- default_models.yaml: add paddle.PP-OCRv6 det+rec (tiny/small/medium), rec has no dict_url (dict from yml)

- test_engine.py: add EngineType.PADDLE to v6 det/rec parametrize

- Verified: v6 paddle tests pass; v4/v5 paddle regression tests pass

* refactor(python): revert have_key workaround, use dict_url for paddle v6 rec

Now that dict files are available on RapidAI/RapidOCR, revert the have_key/get_character_list workaround that read character_dict from inference.yml. Add dict_url to paddle v6 rec entries pointing to the official dict files.

- paddle/main.py: have_key returns False, get_character_list returns [], remove yml_path logic

- default_models.yaml: add dict_url to paddle v6 rec (tiny/small/medium)

- init_predictor and device_config v6 branches remain (required for PIR format)

python/tests/test_engine.py

@@ -143,7 +143,7 @@ def test_engine_tensorrt():
 
 @mark.parametrize(
     "engine_type",
-    [EngineType.ONNXRUNTIME, EngineType.OPENVINO],
+    [EngineType.ONNXRUNTIME, EngineType.OPENVINO, EngineType.PADDLE],
 )
 def test_ppocrv6_det_small(engine_type):
     engine = RapidOCR(
@@ -161,7 +161,7 @@ def test_ppocrv6_det_small(engine_type):
 
 @mark.parametrize(
     "engine_type",
-    [EngineType.ONNXRUNTIME, EngineType.OPENVINO],
+    [EngineType.ONNXRUNTIME, EngineType.OPENVINO, EngineType.PADDLE],
 )
 def test_ppocrv6_rec_small(engine_type):
     engine = RapidOCR(