test(api): add universal DeepPot C/C++ API tests (deepmodeling#5538)

Problem
- Issue deepmodeling#3905 asks for universal C/C++ API coverage instead of one-off
backend-specific DeepPot tests.
- A first pass should stay focused and avoid rewriting the existing
large API test suite.

Change
- Add shared reference data for the common DeepPot water fixture.
- Add parameterized C++ API tests for metadata and atomic inference
across TensorFlow, PyTorch, PT-Expt, JAX, and Paddle when those
backends/artifacts are available.
- Add matching C API tests using `DP_DeepPotCompute2` /
`DP_DeepPotComputef2` and link torch in the C test target so PT-Expt
guards are detected consistently.
- After deepmodeling#5544 fixed PyTorch type-map separators, require exact type-map
metadata again and tighten the remaining PyTorch DeepTensor type-map
test similarly.

Verification
- `uvx pre-commit run --files source/api_c/tests/CMakeLists.txt
source/api_c/tests/test_deeppot_universal.cc
source/api_cc/tests/test_deeppot_universal.cc
source/tests/infer/deeppot_universal_data.h
source/api_c/tests/test_deeppot_a_ptexpt.cc
source/api_cc/tests/test_deepdipole_pt.cc`
- Local full CTest was not run because this workspace does not have a
C++ backend dependency installed; the new tests skip unavailable backend
artifacts and should be exercised by the existing C++ test job after
generated models are prepared.

Refs deepmodeling#3905

Authored by OpenClaw (model: custom-chat-jinzhezeng-group/gpt-5.5)

---------

Co-authored-by: Jinzhe Zeng <jinzhe.zeng@ustc.edu.cn>

Author: njzjz-bot

source/api_c/tests/CMakeLists.txt

@@ -16,6 +16,10 @@ if(ENABLE_TENSORFLOW)
 endif()
 if(ENABLE_PYTORCH)
   target_compile_definitions(runUnitTests_c PRIVATE BUILD_PYTORCH)
+  # Link torch so __has_include(<torch/csrc/inductor/...>) succeeds and
+  # BUILD_PT_EXPT is set for the test binary; otherwise pt_expt tests all
+  # GTEST_SKIP() with "PyTorch support is not enabled".
+  target_link_libraries(runUnitTests_c PRIVATE "${TORCH_LIBRARIES}")
 endif()
 if(ENABLE_JAX)
   target_compile_definitions(runUnitTests_c PRIVATE BUILD_JAX)