feat(jacobian_lens): add artifact registry + short-name resolution in from_pretrained

[mukund1985]

Closes #1536.

What

Adds jacobian_lens_registry.json bundling 37 pre-fitted J-lens artifacts from neuronpedia/jacobian-lens, and teaches JacobianLens.from_pretrained to resolve short model names and Hugging Face model IDs automatically.

Before (users had to know the full Hub subpath):

JacobianLens.from_pretrained(
    "neuronpedia/jacobian-lens",
    filename="gemma-2-2b/jlens/Salesforce-wikitext/gemma-2-2b_jacobian_lens.pt",
)

After (both of these work):

JacobianLens.from_pretrained("gemma-2-2b")
JacobianLens.from_pretrained("google/gemma-2-2b")

Resolution order

1. Local .pt file — unchanged
2. Local directory — unchanged
3. Registry short name or HF model ID alias — resolved to neuronpedia/jacobian-lens + exact subpath
4. Explicit Hub repo + filename kwarg — unchanged (fully backward-compatible)

Registry coverage (37 models)

• Gemma 2 (2b / 9b / 27b, base + instruct)
• Gemma 3 (270m / 1b / 4b / 12b / 27b, base + instruct)
• Gemma 4 (31b / e2b / e4b)
• GPT-2 Small (aliases: gpt2, openai-community/gpt2), GPT-OSS 20B
• Llama 3.1 (8b base + instruct), Llama 3.3 (70b instruct)
• OLMo 3 (7b / 32b), Pythia 70M-deduped
• Qwen 2.5 (7b-it), Qwen 3 (1.7b / 4b / 8b / 14b / 32b), Qwen 3.5 (0.8b / 2b / 4b / 9b / 27b)

The registry JSON is generated from neuronpedia/jacobian-lens sibling list and includes the exact filenames (including the naming irregularities in Gemma 3 base -pt suffix and Gemma 4 uppercase size suffix).

Tests

9 new unit tests in TestRegistry:

• Registry JSON validity and required-field checks
• _resolve_registry_entry by short name and by HF model ID alias
• Unknown model returns None (passthrough to explicit Hub path)
• from_pretrained short-name resolution end-to-end
• from_pretrained HF alias → same artifact as short name
• Unknown name forwards repo_id + filename kwargs unchanged (backward compat)
• Registry filename wins over explicit filename kwarg when name resolves
• GPT-2's three entry points (gpt2-small / gpt2 / openai-community/gpt2) all resolve to the same file

[mukund1985]

Hey @jlarson4 — happy to have a review when you get a chance. Let me know if you want the registry to carry any additional metadata (n_prompts, dtype) or if the alias coverage needs adjusting for any of the models.

[jlarson4]

This looks good to my eyes @mukund1985, I will let CI finish its thing and then merge

[mukund1985]

@jlarson4 CI is all green — 22 checks passed, ready to merge whenever you are.