Enable local TXT2KG + uncertainty-aware LLM with EDFL/ISR

[leochlon]

Fixed import path
Corrected torch_geometric.nn.LLM → torch_geometric.llm.models.LLM to match the upstream module layout and avoid ImportError.

Local TXT2KG support
Added --use_local_txt2kg flag so users can choose between OpenAI/NIM APIs and local Hugging Face models for knowledge graph extraction. Enables fully offline pipelines, avoids API costs, and improves reproducibility.

Checkpoint validation
Properly validates cached triples when switching between local vs. API models. Prevents stale or mismatched KG states from silently propagating into training/inference.

GPU utilization
Passes n_gpus parameter to TXT2KG’s internal LLM, ensuring multi-GPU hardware is actually used.

Uncertainty-aware LLM
Extended LLM(..., uncertainty_estim=True) to compute EDFL/B2T/ISR metrics before generation:

Returns per-item uncertainty metrics: ISR, Δ̄, B2T, RoH bound, priors.
Optionally abstains ("[ABSTAIN]") if ISR < threshold.
During training, masks labels for low-ISR items, enabling GNN+LLM fine-tuning with calibrated refusal rather than random guessing
tests

RAG_TEST=1 pytest test/llm/models/test_llm.py::test_llm_uncertainty -v

[puririshi98]

can you add a copypastable string for the pip install users should use to get it set up

[codecov]

Codecov Report

❌ Patch coverage is 17.64706% with 112 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.89%. Comparing base (c211214) to head (acad83c).
⚠️ Report is 128 commits behind head on master.

Files with missing lines	Patch %	Lines
torch_geometric/llm/models/llm.py	17.96%	105 Missing ⚠️
torch_geometric/llm/models/txt2kg.py	12.50%	7 Missing ⚠️

❌ Your patch check has failed because the patch coverage (17.64%) 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             @@
##           master   #10480      +/-   ##
==========================================
- Coverage   86.11%   84.89%   -1.23%     
==========================================
  Files         496      510      +14     
  Lines       33655    36070    +2415     
==========================================
+ Hits        28981    30620    +1639     
- Misses       4674     5450     +776     

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