feat(tf2): add eager TensorFlow array backend (deepmodeling#5598)

## Summary
- vendor ndtensorflow under deepmd/_vendors and add a TensorFlow eager
Array API backend under deepmd/tf2
- implement tf2 model wrappers, tf.function SavedModel export/deep-eval
glue, and backend registration for .savedmodel
- replace jax/jax2tf TensorFlow helper implementations with tf2
compatibility exports
- add focused tf2 consistency tests for eager and tf.function model
paths

## Tests
- ruff check .
- ruff format .
- pytest source/tests/consistent/test_tf2_backend.py -q
- manual SavedModel export/load smoke test

Note: local pre-commit hook attempted to fetch astral-sh/ruff-pre-commit
and timed out on GitHub port 443; the commit was created with
--no-verify after running the checks above manually.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a TensorFlow 2 eager backend with SavedModel inference plus TF2
model/descriptor/fitting wrappers (energy/dipole/polar/DOS/property).
* Introduced TF2 neighbor-list construction, region/PBC geometry
utilities, and output/ghost-atom aggregation.
* Expanded the TensorFlow-backed Array API with namespace, FFT, and
linear algebra utilities.
* **Bug Fixes**
  * Improved the non-eager TensorFlow compatibility error message.
* **Refactor**
* Converted multiple JAX2TF modules into TF2 compatibility shims that
re-export TF2 implementations.
* **Tests**
  * Added TF2 consistency coverage, including subprocess-based checks.
* **Chores**
  * Added license headers/docs and updated lint configuration.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Jinzhe Zeng <njzjz@qq.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: njzjz-bot (driven by OpenClaw (model: custom-chat-jinzhezeng-group/gpt-5.5))[bot] <48687836+njzjz-bot@users.noreply.github.com>

Author: 3 people

.github/workflows/test_python.yml

@@ -63,12 +63,36 @@ jobs:
           DP_CI_IMPORT_PADDLE_BEFORE_TF: 1
           FLAGS_use_stride_compute_kernel: 0
       - name: Test TF2 eager mode
-        run: pytest --cov=deepmd --cov-append source/tests/consistent/io/test_io.py source/jax2tf_tests
+        run: |
+          run_pytest_allow_no_tests() {
+            set +e
+            pytest "$@"
+            local status=$?
+            set -e
+            if [ "$status" -eq 5 ]; then
+              # pytest-split may leave an individual shard with no selected
+              # tests after path/-k filtering. Other shards still cover the
+              # selected tests, so do not fail the whole matrix for exit 5.
+              return 0
+            fi
+            return "$status"
+          }
+
+          run_pytest_allow_no_tests --cov=deepmd --cov-append \
+            source/tests/consistent/io/test_io.py \
+            source/jax2tf_tests \
+            --splits 12 \
+            --group ${{ matrix.group }}
+          run_pytest_allow_no_tests --cov=deepmd --cov-append \
+            source/tests/consistent \
+            -k tf2 \
+            --splits 12 \
+            --group ${{ matrix.group }}
         env:
           NUM_WORKERS: 0
           DP_TEST_TF2_ONLY: 1
           DP_DTYPE_PROMOTION_STRICT: 1
-        if: matrix.group == 1
+          DP_CI_IMPORT_PADDLE_BEFORE_TF: 1
       - run: mv .test_durations .test_durations_${{ matrix.group }}
       - name: Upload partial durations
         uses: actions/upload-artifact@v7

deepmd/_vendors/__init__.py

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: LGPL-3.0-or-later
+"""Vendored third-party modules used by DeePMD-kit."""

deepmd/_vendors/ndtensorflow/__init__.py

@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: LGPL-3.0-or-later
+from __future__ import (
+    annotations,
+)
+
+from typing import (
+    Final,
+)
+
+from . import (
+    fft,
+    linalg,
+)
+from ._array import (
+    Array,
+)
+from ._info import (
+    __array_namespace_info__,
+)
+from ._namespace import *
+from ._namespace import __all__ as _namespace_all
+
+__array_api_version__: Final = "2025.12"
+
+__all__ = sorted(
+    set(_namespace_all)
+    | {
+        "Array",
+        "__array_api_version__",
+        "__array_namespace_info__",
+        "fft",
+        "linalg",
+    }
+)
+
+
+def __dir__() -> list[str]:
+    return __all__