Fix ADME tests

[gbg141]

Make ADME dataset dependencies (PyTDC, rdkit) lazy imports

tdc and ogb.utils.mol were imported at the top of adme_datasets.py, crashing any dataset load if those packages were missing. Wrapped them in a module-level try/except so the names remain available for test patching when installed, but load_dataset() raises a clear ImportError with install instructions when they are not.

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.03%. Comparing base (f182a43) to head (8278c45).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
topobench/data/loaders/graph/adme_datasets.py	71.42%	2 Missing ⚠️

❌ Your patch status has failed because the patch coverage (71.42%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #344      +/-   ##
==========================================
- Coverage   94.06%   94.03%   -0.04%     
==========================================
  Files         206      206              
  Lines        8726     8732       +6     
==========================================
+ Hits         8208     8211       +3     
- Misses        518      521       +3     

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