test(suite): exhaustive test suite expansion (~559 tests)

[johnmarktaylor91]

Summary

• Add 64 new toy model classes and tests covering attention/transformers, containers (ModuleList/Dict), conditional/dynamic ops, normalization variants (LayerNorm/GroupNorm/InstanceNorm), Conv1d/Conv3d, residual blocks, parameter sharing, in-place chains, type casting, scalar/broadcasting, packed sequences, custom autograd, exemption registry stress tests, architecture patterns (VAE, GAN, UNet, TCN, PixelShuffle, PointNet, ActorCritic, TwoTower, DepthEstimator), and 16 adversarial edge-case models targeting specific torchlens code paths
• Add 12 new real-world model tests: DistilBERT, ELECTRA, MobileViT, MoE (built-in), T5, BART, RoBERTa, BLIP, Whisper, ViT-MAE, Conformer, SentenceTransformer
• Merge test_real_world_models_slow.py into test_real_world_models.py organized by architecture/modality, using @pytest.mark.slow for heavy tests
• Register slow pytest marker in pyproject.toml
• Add 4 new fixtures (seq_input, token_input, input_3d, input_1d_seq) and 5 vis output subdirs

Test plan

• pytest tests/test_toy_models.py -v --timeout=120 — verify new toy model tests
• pytest tests/test_real_world_models.py -m "not slow" -v --timeout=300 — verify fast real-world tests
• pytest tests/test_real_world_models.py -m "slow" -v --timeout=600 — verify slow real-world tests
• pytest tests/ -v --timeout=600 — full regression
• Review adversarial edge-case failures and decide which need exemptions vs xfail vs fixes