fix(rdkit): avoid deprecated explicit valence API (#969)

Problem
- RDKit deprecated `Atom.GetExplicitValence()` in recent releases, which
makes dpdata CI emit a deprecation warning.
- `dpdata.rdkit.sanitize.get_explicit_valence()` still called the
deprecated API directly.

Change
- Prefer `Atom.GetValence(Chem.ValenceType.EXPLICIT)` when available,
with a fallback to `Atom.GetExplicitValence()` for compatibility with
older RDKit versions.
- Add a focused unit test that verifies both the new-API path and the
legacy fallback path without requiring RDKit at test time.

Notes
- Fixes #968.
- Tests run: `python3 -m unittest tests/test_rdkit_sanitize.py`

Authored by OpenClaw (model: gpt-5.4)


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

## Summary by CodeRabbit

## Release Notes

* **Chores**
* Enhanced compatibility by adding automatic version detection and
fallback support for different RDKit library versions to ensure
consistent behavior.

* **Tests**
* Added comprehensive test coverage to verify valence calculations work
correctly across different RDKit library versions.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: njzjz-bot

dpdata/rdkit/sanitize.py

@@ -10,11 +10,18 @@ def get_explicit_valence(atom, verbose=False):
         sum([bond.GetBondTypeAsDouble() for bond in atom.GetBonds()])
     )
     try:
-        exp_val = atom.GetExplicitValence()
+        try:
+            from rdkit import Chem
+
+            exp_val = atom.GetValence(Chem.ValenceType.EXPLICIT)
+            valence_method = "GetValence(Chem.ValenceType.EXPLICIT)"
+        except (ImportError, AttributeError, TypeError):
+            exp_val = atom.GetExplicitValence()
+            valence_method = "GetExplicitValence()"
         if exp_val != exp_val_calculated_from_bonds:
             if verbose:
                 print(
-                    f"Explicit valence given by GetExplicitValence() and sum of bond order are inconsistent on {atom.GetSymbol()}{atom.GetIdx() + 1}, using sum of bond order."
+                    f"Explicit valence given by {valence_method} and sum of bond order are inconsistent on {atom.GetSymbol()}{atom.GetIdx() + 1}, using sum of bond order."
                 )
         return exp_val_calculated_from_bonds
     except Exception: